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Sample records for ocean freshwater export

  1. Arctic freshwater export: Status, mechanisms, and prospects

    NASA Astrophysics Data System (ADS)

    Haine, Thomas W. N.; Curry, Beth; Gerdes, Rüdiger; Hansen, Edmond; Karcher, Michael; Lee, Craig; Rudels, Bert; Spreen, Gunnar; de Steur, Laura; Stewart, Kial D.; Woodgate, Rebecca

    2015-02-01

    Large freshwater anomalies clearly exist in the Arctic Ocean. For example, liquid freshwater has accumulated in the Beaufort Gyre in the decade of the 2000s compared to 1980-2000, with an extra ≈ 5000 km3 - about 25% - being stored. The sources of freshwater to the Arctic from precipitation and runoff have increased between these periods (most of the evidence comes from models). Despite flux increases from 2001 to 2011, it is uncertain if the marine freshwater source through Bering Strait for the 2000s has changed, as observations in the 1980s and 1990s are incomplete. The marine freshwater fluxes draining the Arctic through Fram and Davis straits are also insignificantly different. In this way, the balance of sources and sinks of freshwater to the Arctic, Canadian Arctic Archipelago (CAA), and Baffin Bay shifted to about 1200 ± 730 km3 yr- 1 freshening the region, on average, during the 2000s. The observed accumulation of liquid freshwater is consistent with this increased supply and the loss of freshwater from sea ice. Coupled climate models project continued freshening of the Arctic during the 21st century, with a total gain of about 50,000 km3 for the Arctic, CAA, and Baffin Bay (an increase of about 50%) by 2100. Understanding of the mechanisms controlling freshwater emphasizes the importance of Arctic surface winds, in addition to the sources of freshwater. The wind can modify the storage, release, and pathways of freshwater on timescales of O(1-10) months. Discharges of excess freshwater through Fram or Davis straits appear possible, triggered by changes in the wind, but are hard to predict. Continued measurement of the fluxes and storage of freshwater is needed to observe changes such as these.

  2. Changing Arctic Ocean freshwater pathways.

    PubMed

    Morison, James; Kwok, Ron; Peralta-Ferriz, Cecilia; Alkire, Matt; Rigor, Ignatius; Andersen, Roger; Steele, Mike

    2012-01-01

    Freshening in the Canada basin of the Arctic Ocean began in the 1990s and continued to at least the end of 2008. By then, the Arctic Ocean might have gained four times as much fresh water as comprised the Great Salinity Anomaly of the 1970s, raising the spectre of slowing global ocean circulation. Freshening has been attributed to increased sea ice melting and contributions from runoff, but a leading explanation has been a strengthening of the Beaufort High--a characteristic peak in sea level atmospheric pressure--which tends to accelerate an anticyclonic (clockwise) wind pattern causing convergence of fresh surface water. Limited observations have made this explanation difficult to verify, and observations of increasing freshwater content under a weakened Beaufort High suggest that other factors must be affecting freshwater content. Here we use observations to show that during a time of record reductions in ice extent from 2005 to 2008, the dominant freshwater content changes were an increase in the Canada basin balanced by a decrease in the Eurasian basin. Observations are drawn from satellite data (sea surface height and ocean-bottom pressure) and in situ data. The freshwater changes were due to a cyclonic (anticlockwise) shift in the ocean pathway of Eurasian runoff forced by strengthening of the west-to-east Northern Hemisphere atmospheric circulation characterized by an increased Arctic Oscillation index. Our results confirm that runoff is an important influence on the Arctic Ocean and establish that the spatial and temporal manifestations of the runoff pathways are modulated by the Arctic Oscillation, rather than the strength of the wind-driven Beaufort Gyre circulation. PMID:22222749

  3. Atmospheric and oceanic freshwater transport during weak Atlantic overturning circulation

    NASA Astrophysics Data System (ADS)

    Lohmann, Gerrit

    2003-10-01

    Oceanic and atmospheric freshwater transports are analyzed in a numerical experiment where induced freshwater in the North Atlantic slowed the thermohaline circulation (THC). During times of weak Atlantic overturning circulation, it is found that the Intertropical Convergence Zone moves southward and trade winds at tropical latitudes increase, resulting in enhanced water vapor export out of the Atlantic catchment area. The experiment reveals furthermore that the oceanic freshwater transport amounts to a stabilizing effect of similar magnitude to the atmospheric effect. It is argued that the modeled response can be used as a fingerprint for the detection of THC changes documented in the paleoclimatic record or related recent climate change.

  4. Arctic Ocean basin liquid freshwater storage trend 1992-2012

    NASA Astrophysics Data System (ADS)

    Rabe, B.; Karcher, M.; Kauker, F.; Schauer, U.; Toole, J. M.; Krishfield, R. A.; Pisarev, S.; Kikuchi, T.; Su, J.

    2014-02-01

    Freshwater in the Arctic Ocean plays an important role in the regional ocean circulation, sea ice, and global climate. From salinity observed by a variety of platforms, we are able, for the first time, to estimate a statistically reliable liquid freshwater trend from monthly gridded fields over all upper Arctic Ocean basins. From 1992 to 2012 this trend was 600±300 km3 yr-1. A numerical model agrees very well with the observed freshwater changes. A decrease in salinity made up about two thirds of the freshwater trend and a thickening of the upper layer up to one third. The Arctic Ocean Oscillation index, a measure for the regional wind stress curl, correlated well with our freshwater time series. No clear relation to Arctic Oscillation or Arctic Dipole indices could be found. Following other observational studies, an increased Bering Strait freshwater import to the Arctic Ocean, a decreased Davis Strait export, and enhanced net sea ice melt could have played an important role in the freshwater trend we observed.

  5. The Role of River Runoff in the Freshwater Budget of the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Rennermalm, A.; Wood, E.; Dery, S.; Weaver, A.

    2005-12-01

    The freshwater export through the Fram Strait is important in governing the strength of the thermohaline circulation in the North Atlantic. Here we address the role of river runoff in the Arctic Ocean freshwater budget and how it in turn may affect the climate system on a larger scale though effects on the thermohaline circulation and sea ice cover. The role of runoff may be important in this regard because the riverine freshwater input is of similar magnitude as the freshwater export through the Fram Strait. An intermediate complexity general climate model (UVic ESCM) is used to conduct a series of experiments examining the role of the large rivers draining into the Arctic Ocean. In addition to studying the sensitivity caused by rivers draining into the Arctic Ocean we also study the rivers draining into Hudson Bay, the freshwater export through the Canadian Archipelago and finally freshwater import through Bering Strait Observations from the last few decades indicate that river runoff has increased into the Arctic Ocean and decreased into Hudson Bay. Our study contributes to understanding the implications of future changes in river runoff into the Arctic Ocean and Hudson Bay, and in better quantifying the importance of freshwater flow through Bering Strait and the Canadian Archipelago.

  6. The response of the central Arctic Ocean stratification to freshwater perturbations

    NASA Astrophysics Data System (ADS)

    Pemberton, P.; Nilsson, J.

    2016-01-01

    Using a state-of-the-art coupled ice-ocean-circulation model, we perform a number of sensitivity experiments to examine how the central Arctic Ocean stratification responds to changes in river runoff and precipitation. The simulations yield marked changes in the cold halocline and the Arctic Atlantic layer. Increased precipitation yields a warming of the Atlantic layer, which primarily is an advective signal, propagated through the St. Anna Trough, reflecting air-sea heat flux changes over the Barents Sea. As the freshwater supply is increased, the anticyclonic Beaufort Gyre is weakened and a greater proportion of the Arctic Ocean freshwater is exported via the Fram Strait, with nearly compensating export decreases through the Canadian Arctic Archipelago. The corresponding reorganization of the freshwater pool appears to be controlled by advective processes, rather than by the local changes in the surface freshwater flux. A simple conceptual model of the Arctic Ocean, based on a geostrophically controlled discharge of the low-salinity water, is introduced and compared with the simulations. Key predictions of the conceptual model are that the halocline depth should decrease with increasing freshwater input and that the Arctic Ocean freshwater storage should increase proportionally to the square root of the freshwater input, which are in broad qualitative agreement with the sensitivity experiments. However, the model-simulated rate of increase of the freshwater storage is weaker, indicating that effects related to wind forcing and rerouting of the freshwater-transport pathways play an important role for the dynamics of the Arctic Ocean freshwater storage.

  7. Arctic Ocean Freshwater: How Robust are Model Simulations

    NASA Technical Reports Server (NTRS)

    Jahn, A.; Aksenov, Y.; deCuevas, B. A.; deSteur, L.; Haekkinen, S.; Hansen, E.; Herbaut, C.; Houssais, M.-N.; Karcher, M.; Kauker, F.; Lique, C.; Nguyen, A.; Pemberton, P.; Worthen, D.; Zhang, J.

    2012-01-01

    The Arctic freshwater (FW) has been the focus of many modeling studies, due to the potential impact of Arctic FW on the deep water formation in the North Atlantic. A comparison of the hindcasts from ten ocean-sea ice models shows that the simulation of the Arctic FW budget is quite different in the investigated models. While they agree on the general sink and source terms of the Arctic FW budget, the long-term means as well as the variability of the FW export vary among models. The best model-to-model agreement is found for the interannual and seasonal variability of the solid FW export and the solid FW storage, which also agree well with observations. For the interannual and seasonal variability of the liquid FW export, the agreement among models is better for the Canadian Arctic Archipelago (CAA) than for Fram Strait. The reason for this is that models are more consistent in simulating volume flux anomalies than salinity anomalies and volume-flux anomalies dominate the liquid FW export variability in the CAA but not in Fram Strait. The seasonal cycle of the liquid FW export generally shows a better agreement among models than the interannual variability, and compared to observations the models capture the seasonality of the liquid FW export rather well. In order to improve future simulations of the Arctic FW budget, the simulation of the salinity field needs to be improved, so that model results on the variability of the liquid FW export and storage become more robust.

  8. Global estimation of freshwater fluxes and freshwater oceanic transport from satellite data

    SciTech Connect

    Gautier, C.; Peterson, P.; Jones, C.

    1996-12-01

    The exchange of moisture and heat fluxes across the ocean-atmosphere interface exerts a strong influence on the oceanic and atmospheric circulations, and therefore on the maintenance of the climate system equilibrium. Observational measurements of these fluxes over large areas of the ocean`s surface are limited by the lack of in-situ data. This paper reports research efforts to estimate the freshwater budget and freshwater oceanic transport using remotely sensed data. Six years (1988--1993) of surface evaporation estimated with satellite and in-situ data re combined with satellite-derived precipitation to compute the freshwater budget and freshwater oceanic transport. The interannual variability of the freshwater budget and oceanic transport eliminates are examined for two contrasting events: the La Nina of 1988--89 and the El Nino condition during 1991--92, one of the longest El Nino episodes on record. Possible implications for future climate change are discussed.

  9. Changes in Arctic freshwater export: a new proxy from 30 years of hydrographic surveys in the Labrador Sea

    NASA Astrophysics Data System (ADS)

    Florindo-Lopez, Cristian; Holliday, N. Penny; Bacon, Sheldon; Aksenov, Yevgeny

    2015-04-01

    The Arctic Ocean is the most rapidly changing environment in the globe. One of the observed changes is a significant increase in the freshwater storage at the region. It is believed that a large and rapid export of this freshwater into the North Atlantic could potentially affect high-latitude dense water formation, the overturning circulation and climate. However, Arctic freshwater fluxes to the Labrador Sea are poorly known and observational time series are not available beyond the last decade. We present a new insight in Labrador shelf dynamics, which allows us to connect locally-observed property variability to net Arctic freshwater exports west of Greenland. By combining the high-resolution (1/12 degree) NEMO model and hydrographic observations at the Labrador Shelf, we describe two major components of the shelf circulation. On the one hand the Labrador Current fills the shelf with Arctic originated waters. On the other hand, the Hudson Strait Outflow generates a very distinctive inshore buoyancy-driven flow. This newly described current is geographically and dynamically independent of the Labrador Current, and we are able to separate it from the waters of Arctic origin which flow further offshore. We apply this methodology to a Labrador hydrographic time series of over 30 years in length, allowing us to generate a proxy that we can use to assess the variability of Arctic freshwater export west of Greenland for over 30 years. We show that on decadal timescales, periods of decreased freshwater export on the Labrador Shelf coincide with periods of increased Arctic freshwater content.

  10. Deep-ocean origin of the freshwater eels

    PubMed Central

    Inoue, Jun G.; Miya, Masaki; Miller, Michael J.; Sado, Tetsuya; Hanel, Reinhold; Hatooka, Kiyotaka; Aoyama, Jun; Minegishi, Yuki; Nishida, Mutsumi; Tsukamoto, Katsumi

    2010-01-01

    Of more than 800 species of eels of the order Anguilliformes, only freshwater eels (genus Anguilla with 16 species plus three subspecies) spend most of their lives in freshwater during their catadromous life cycle. Nevertheless, because their spawning areas are located offshore in the open ocean, they migrate back to their specific breeding places in the ocean, often located thousands of kilometres away. The evolutionary origin of such enigmatic behaviour, however, remains elusive because of the uncertain phylogenetic position of freshwater eels within the principally marine anguilliforms. Here, we show strong evidence for a deep oceanic origin of the freshwater eels, based on the phylogenetic analysis of whole mitochondrial genome sequences from 56 species representing all of the 19 anguilliform families. The freshwater eels occupy an apical position within the anguilliforms, forming a highly supported monophyletic group with various oceanic midwater eel species. Moreover, reconstruction of the growth habitats on the resulting tree unequivocally indicates an origination of the freshwater eels from the midwater of the deep ocean. This shows significant concordance with the recent collection of mature adults of the Japanese eel in the upper midwater of the Pacific, suggesting that they have retained their evolutionary origin as a behavioural trait in their spawning areas. PMID:20053660

  11. New Production Regulates Export Stoichiometry in the Ocean

    PubMed Central

    Tamelander, Tobias; Reigstad, Marit; Olli, Kalle; Slagstad, Dag; Wassmann, Paul

    2013-01-01

    The proportion in which carbon and growth-limiting nutrients are exported from the oceans productive surface layer to the deep sea is a crucial parameter in models of the biological carbon pump. Based on >400 vertical flux observations of particulate organic carbon (POC) and nitrogen (PON) from the European Arctic Ocean we show the common assumption of constant C:N stoichiometry not to be met. Exported POC:PON ratios exceeded the classical Redfield atomic ratio of 6.625 in the entire region, with the largest deviation in the deep Central Arctic Ocean. In this part the mean exported POC:PON ratio of 9.7 (a:a) implies c. 40% higher carbon export compared to Redfield-based estimates. When spatially integrated, the potential POC export in the European Arctic was 1030% higher than suggested by calculations based on constant POC:PON ratios. We further demonstrate that the exported POC:PON ratio varies regionally in relation to nitrate-based new production over geographical scales that range from the Arctic to the subtropics, being highest in the least productive oligotrophic Central Arctic Ocean and subtropical gyres. Accounting for variations in export stoichiometry among systems of different productivity will improve the ability of models to resolve regional patterns in carbon export and, hence, the oceans contribution to the global carbon cycle will be predicted more accurately. PMID:23342065

  12. Freshwater transport in the coupled ocean-atmosphere system: a passive ocean

    NASA Astrophysics Data System (ADS)

    Ferreira, David; Marshall, John

    2015-07-01

    Conservation of water demands that meridional ocean and atmosphere freshwater transports (FWT) are of equal magnitude but opposite in direction. This suggests that the atmospheric FWT and its associated latent heat (LH) transport could be thought of as a "coupled ocean/atmosphere mode." But what is the true nature of this coupling? Is the ocean passive or active? Here, we analyze a series of simulations with a coupled ocean-atmosphere-sea ice model employing highly idealized geometries but with markedly different coupled climates and patterns of ocean circulation. Exploiting streamfunctions in specific humidity coordinates for the atmosphere and salt coordinates for the ocean to represent FWT in their respective medium, we find that atmospheric FWT/LH transport is essentially independent of the ocean state. Ocean circulation and salinity distribution adjust to achieve a return freshwater pathway demanded of them by the atmosphere. So, although ocean and atmosphere FWTs are indeed coupled by mass conservation, the ocean is a passive component acting as a reservoir of freshwater.

  13. Dissolved organic carbon pools and export from the coastal ocean

    NASA Astrophysics Data System (ADS)

    Barrn, Cristina; Duarte, Carlos M.

    2015-10-01

    The distribution of dissolved organic carbon (DOC) concentration across coastal waters was characterized based on the compilation of 3510 individual estimates of DOC in coastal waters worldwide. We estimated the DOC concentration in the coastal waters that directly exchange with open ocean waters in two different ways, as the DOC concentration at the edge of the shelf break and as the DOC concentration in coastal waters with salinity close to the average salinity in the open ocean. Using these estimates of DOC concentration in the coastal waters that directly exchange with open ocean waters, the mean DOC concentration in the open ocean and the estimated volume of water annually exchanged between coastal and open ocean, we estimated a median SE (and average SE) global DOC export from coastal to open ocean waters ranging from 4.4 1.0 Pg C yr-1 to 27.0 1.8 Pg C yr-1 (7.0 5.8 Pg C yr-1 to 29.0 8.0 Pg C yr-1) depending on the global hydrological exchange. These values correspond to a median and mean median (and average) range between 14.7 3.3 to 90.0 6.0 (23.3 19.3 to 96.7 26.7) Gg C yr-1 per km of shelf break, which is consistent with the range between 1.4 to 66.1 Gg C yr-1 per km of shelf break of available regional estimates of DOC export. The estimated global DOC export from coastal to open ocean waters is also consistent with independent estimates of the net metabolic balance of the coastal ocean. The DOC export from the coastal to the open ocean is likely to be a sizeable flux and is likely to be an important term in the carbon budget of the open ocean, potentially providing an important subsidy to support heterotrophic activity in the open ocean.

  14. Residence time of the freshwater component in the Arctic Ocean

    SciTech Connect

    Ostlund, H.G.

    1982-03-20

    The time function of bomb tritium concentrations in river runoff to the Arctic Ocean has been reconstructed from published data on tritium in precipatatio 1959--1975. Tritium measurements on oceanic samples through the haloclinie exhibit strong linear relatioships between tritium concetrations (TU values) and salinity. These wates thus look like binary mixtures of Atlantic source water and freshwater runoff. Combining these data, the vintage of the freshwater component in the Arctic Basin has been determined assuming no other major tritium source. The relation indicates the average age of the freshwater component to be 11 +- 1 years in the Namsen Basin and the outflow and somewhat higher in the Canada Basin. According to ttitium/salinity data, a surface layer of 10--60 m is affected by sea ice melting and freezing in the Nansen Basin, and the thickness of this layer increases to 150--170 m toward the Canada Basin. There is tritium also in the deep waters, the unumixed Atlantic water, which points at residence times for that water not to exceed 17 years.

  15. Mass, heat and freshwater fluxes in the South Indian Ocean

    NASA Technical Reports Server (NTRS)

    Fu, Lee-Lueng

    1986-01-01

    Six hydrographic sections were used to examine the circulation and property fluxes in the South Indian Ocean from 10 to 32 deg S. The calculations were made by applying an inverse method to the data. In the interior of the South Indian Ocean, the geostrophic flow is generally northward. At 18 deg S, the northward interior mass flux is balanced by the southward Ekman mass flux at the surface, whereas at 32 deg S the northward interior mass flux is balanced by the southward mass flux of the Agulhas Current. There is a weak, southward mass flux of 6 x 10 to the 9th kg/s in the Mozambique Channel. The rate of water exchange between the Pacific Ocean and the Indian Ocean is dependent on the choice of the initial reference level used in the inverse calculation. The choice of 1500 m, the depth of the deep oxygen minimum, has led to a flux of water from the Pacific Ocean to the Indian Ocean at a rate of 6.6 x 10 to the 9th kg/s. Heat flux calculations indicate that the Indian Ocean is exporting heat to the rest of the world's oceans at a rate of -0.69 x 10 to the 15th W at 18 deg S and -0.25 x 10 to the 15th W at 32 deg S (negative values being southward).

  16. On the relationship between Nd isotopic composition and ocean overturning circulation in idealized freshwater discharge events

    NASA Astrophysics Data System (ADS)

    Rempfer, Johannes; Stocker, Thomas F.; Joos, Fortunat; Dutay, Jean-Claude

    2012-09-01

    Using a cost-efficient climate model, the effect of changes in overturning circulation on neodymium isotopic composition,?Nd, is systematically examined for the first time. Idealized sequences of abrupt climate changes are induced by the application of periodic freshwater fluxes to the North Atlantic (NA) and the Southern Ocean (SO), thus mainly affecting either the formation of North Atlantic Deep Water (NADW) or Antarctic Bottom Water (AABW). Variations in ?Nd reflect weakening and strengthening of the formation of NADW and AABW, changes in ?Ndof end-members are relatively small. Relationships between?Nd and the strength of NADW or AABW are more pronounced for AABW than for NADW. Atlantic patterns of variations in ?Nd systematically differ between NA and SO experiments. Additionally, the signature of changes in ?Nd in the Atlantic and the Pacific is alike in NA but opposite in SO experiments. Discrimination between NA and SO experiments is therefore possible based on the Atlantic pattern of variations in ?Nd and the contrariwise behavior of ?Nd in the Atlantic and the Pacific. In further experiments we examined the effect of variations in magnitudes of particle export fluxes. Within the examined range, and although settling particles represent the only sink of Nd, their effects on ?Nd are relatively small. Our results confirm the large potential of ?Nd as a paleocirculation tracer but also indicate its limitations of quantitative reconstructions of changes in the Atlantic Meridional Ocean Circulation.

  17. An assessment of the Arctic Ocean in a suite of interannual CORE-II simulations. Part II: Liquid freshwater

    NASA Astrophysics Data System (ADS)

    Wang, Qiang; Ilicak, Mehmet; Gerdes, Rüdiger; Drange, Helge; Aksenov, Yevgeny; Bailey, David A.; Bentsen, Mats; Biastoch, Arne; Bozec, Alexandra; Böning, Claus; Cassou, Christophe; Chassignet, Eric; Coward, Andrew C.; Curry, Beth; Danabasoglu, Gokhan; Danilov, Sergey; Fernandez, Elodie; Fogli, Pier Giuseppe; Fujii, Yosuke; Griffies, Stephen M.; Iovino, Doroteaciro; Jahn, Alexandra; Jung, Thomas; Large, William G.; Lee, Craig; Lique, Camille; Lu, Jianhua; Masina, Simona; Nurser, A. J. George; Rabe, Benjamin; Roth, Christina; Salas y Mélia, David; Samuels, Bonita L.; Spence, Paul; Tsujino, Hiroyuki; Valcke, Sophie; Voldoire, Aurore; Wang, Xuezhu; Yeager, Steve G.

    2016-03-01

    The Arctic Ocean simulated in 14 global ocean-sea ice models in the framework of the Coordinated Ocean-ice Reference Experiments, phase II (CORE-II) is analyzed in this study. The focus is on the Arctic liquid freshwater (FW) sources and freshwater content (FWC). The models agree on the interannual variability of liquid FW transport at the gateways where the ocean volume transport determines the FW transport variability. The variation of liquid FWC is induced by both the surface FW flux (associated with sea ice production) and lateral liquid FW transport, which are in phase when averaged on decadal time scales. The liquid FWC shows an increase starting from the mid-1990s, caused by the reduction of both sea ice formation and liquid FW export, with the former being more significant in most of the models. The mean state of the FW budget is less consistently simulated than the temporal variability. The model ensemble means of liquid FW transport through the Arctic gateways compare well with observations. On average, the models have too high mean FWC, weaker upward trends of FWC in the recent decade than the observation, and low consistency in the temporal variation of FWC spatial distribution, which needs to be further explored for the purpose of model development.

  18. Oceanic export of relict carbon by small mountainous rivers

    NASA Astrophysics Data System (ADS)

    Komada, Tomoko; Druffel, Ellen R. M.; Trumbore, Susan E.

    2004-04-01

    Small mountainous rivers (SMR) export globally significant quantities of particulate organic carbon (POC) to the oceans, the composition of which may be distinct from POC delivered by major world rivers. To better constrain the controls on the ?14C signatures of POC suspended in SMR, we examined the temporal variability of ?14C and ?13C of POC suspended in the Santa Clara River, a SMR in California, USA. Our data suggest mixing of bedrock and contemporary soil, which can be applied to other SMR in contrasting climate zones and with varying land cover. The data also suggest that chemical denudation is incomplete, but effective to the point that only the most recalcitrant moieties of the parent POC are exported. We further propose sediment yield as a potentially useful proxy for the ?14C of riverine POC. A preliminary analysis of the existing data for a spectrum of rivers supports this hypothesis.

  19. Methods for freshwater riverine input into regional ocean models

    NASA Astrophysics Data System (ADS)

    Herzfeld, M.

    2015-06-01

    The input of freshwater at the coast in regional models is a non-trivial exercise that has been studied extensively in the past. Several issues are of relevance; firstly, estuaries process water properties along their length, so that while freshwater may enter at the estuary head, it is no longer fresh at the mouth. Secondly, models create a numerical response that results in excessive upstream or offshore transport compared to what is typically observed. The cause of this has been traced to the lack of landward flow at the coast where freshwater is input. In this study we assess the performance of various methods of freshwater input in coarse resolution regional models where the estuary cannot be explicitly resolved, and present a formulation that attempts to account for upstream flow in the salt wedge and in-estuary mixing that elevates salinity at the mouth.

  20. Arctic sea ice and freshwater sensitivity to the treatment of the atmosphere-ice-ocean surface layer

    NASA Astrophysics Data System (ADS)

    Roy, Franois; Chevallier, Matthieu; Smith, Gregory C.; Dupont, Frdric; Garric, Gilles; Lemieux, Jean-Franois; Lu, Youyu; Davidson, Fraser

    2015-06-01

    Global simulations are presented focusing on the atmosphere-ice-ocean (AIO) surface layer (SL) in the Arctic. Results are produced using an ocean model (NEMO) coupled to two different sea ice models: the Louvain-La-Neuve single-category model (LIM2) and the Los Alamos multicategory model (CICE4). A more objective way to adjust the sea ice-ocean drag is proposed compared to a coefficient tuning approach. The air-ice drag is also adjusted to be more consistent with the atmospheric forcing data set. Improving the AIO SL treatment leads to more realistic results, having a significant impact on the sea ice volume trend, sea ice thickness, and the Arctic freshwater (FW) budget. The physical mechanisms explaining this sensitivity are studied. Improved sea ice drift speeds result in less sea ice accumulation in the Beaufort Sea, correcting a typical ice thickness bias. Sea ice thickness and drag parameters affect how atmospheric stress is transferred to the ocean, thereby influencing Ekman transport and FW retention in the Beaufort Gyre (BG). Increasing sea ice-ocean roughness reduces sea ice growth in winter by reducing ice deformation and lead fractions in the BG. It also increases the total Arctic FW content by reducing sea ice export through Fram Strait. Similarly, increasing air-ice roughness increases the total Arctic FW content by increasing FW retention in the BG.

  1. Revisting the Relation Between Export and Production in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Maiti, K.; Charette, M. A.; Buesseler, K.

    2012-12-01

    Southern Ocean acts as a net sink for atmospheric CO2 mainly due to the phytoplankton uptake of atmospheric CO2 and subsequent downward particle flux of biogenic carbon. Of the organic material generated by primary production of phytoplankton in the surface ocean, most is recycled and a very small fraction is exported and sequestered into the deeper ocean. However surface production and export are often decoupled and the controls on export appear to have important temporal and regional variability that are not directly proportional to local primary production levels. Since very little in situ data was available from this region, most of the estimates of carbon export for the Southern Ocean are derived based on the global relationship between production, export efficiency and temperature by utilizing satellite derived primary production and sea surface temperature data. In the past decade, a number of studies were carried out in the Southern Ocean to look at export production using shallow sediment traps and Thorium-234 based measurements which allows us to re-examines the validity of using the existing relationships between production, export efficiency and temperature to derive carbon export in this region. The existing export production models predict the export efficiency to increase exponentially with increase in primary production. However the in situ flux data is suggestive of a more complex relationship between export and production that may even be inverse i.e. export efficiency increases with decrease in primary production. Comparisons of in situ export rates with modeled rates indicate a two to four fold overestimation of export production by existing models. The primary reason for this could be the fact that most export production models assume a steady state system, which may not apply to a dynamic system like the Southern Ocean, especially since most of the sample collection from this region takes place between October-March when the system is associated with numerous bloom events. Furthermore, unlike the global export models where temperature plays the most dominant role in controlling export, for the colder Southern Ocean with a much narrower range in temperature, it may not be as significant with other factors like grazing intensity, recycling efficiency, high bacterial activity, DOM generation becoming the more dominant factors in controlling the carbon flux. The most important implication of these observations is that the simplest models of export, which predict an increase in particulate carbon flux with increasing surface productivity, may require additional parameters, different weighing of existing parameters, or separate algorithms altogether for different oceanic regimes.

  2. The Annual Cycle of Arctic Ice and Ocean Heat and Freshwater Fluxes, Measured and Modelled

    NASA Astrophysics Data System (ADS)

    Bacon, S.; Aksenov, Y.; Tsubouchi, T.

    2014-12-01

    Paucity of measurements means that quantifying and evaluating the Arctic thermal and hydrological cycles is problematic. For example: atmospheric reanalyses are not well constrained by observations; for river runoff measurements, there are un-gauged flows to consider; and until the relatively recent advent of autonomous measurement systems, ocean measurements outside the summer melt season were rare. We have assembled a complete and continuous Arctic Ocean boundary measurement array from moored installations in four ocean gateways: Fram, Davis and Bering Straits, and the Barents Sea Opening. Occasionally "patching" with coupled ice-ocean general circulation model (GCM) output is required; if so, the output water properties are validated and calibrated against climatology. This approach enables application of inverse modeling methods through the use of conservation constraints, and consequent generation of a set of 12 monthly-mean ocean (including sea ice) fluxes of freshwater and heat spanning a full calendar year. We will present results from a single annual cycle (2005-6). We have also transferred the design of the Arctic Ocean Boundary Array to the GCM environment, where we have calculated the mean annual cycles (from ca. 30-year model runs) both of net surface fluxes (atmosphere-ocean and land-ocean, including sea ice) and equivalent ice and ocean boundary fluxes of freshwater and heat, at two model resolutions (1/4 degree and 1/12 degree global mean) and for two different surface forcing data sets. We will show the resulting comparisons of the mean annual cycles of measured and modeled Arctic freshwater and heat fluxes, and also show the modeled mean annual cycle of heat and freshwater storage. We believe that the integral boundary array formed by sustained measurements in the four named ocean gateways should be a cornerstone of any Arctic environmental monitoring system.

  3. On the proportion of ballast versus non-ballast associated carbon export in the surface ocean

    NASA Astrophysics Data System (ADS)

    Le Moigne, Frédéric A. C.; Sanders, Richard J.; Villa-Alfageme, María; Martin, Adrian P.; Pabortsava, Katsiaryna; Planquette, Hélène; Morris, Paul J.; Thomalla, Sandy J.

    2012-08-01

    The role of biominerals in driving carbon export from the surface ocean is unclear. We compiled surface particulate organic carbon (POC), and mineral ballast export fluxes from 55 different locations in the Atlantic and Southern Oceans. Substantial surface POC export accompanied by negligible mineral export was recorded implying that association with mineral phases is not a precondition for organic export to occur. The proportion of non-mineral associated sinking POC ranged from 0 to 80% and was highest in areas previously shown to be dominated by diatoms. This is consistent with previous estimates showing that transfer efficiency in such regions is low. However we propose that, rather than the low transfer efficiency arising from diatom blooms being inherently characterized by poorly packaged aggregates which are efficiently exported but which disintegrate readily in mid water, it is due to such environments having very high levels of unballasted organic C export.

  4. Hydrographic changes in the Lincoln Sea in the Arctic Ocean with focus on an upper ocean freshwater anomaly between 2007 and 2010

    NASA Astrophysics Data System (ADS)

    Steur, L.; Steele, M.; Hansen, E.; Morison, J.; Polyakov, I.; Olsen, S. M.; Melling, H.; McLaughlin, F. A.; Kwok, R.; Smethie, W. M.; Schlosser, P.

    2013-09-01

    Hydrographic data from the Arctic Ocean show that freshwater content in the Lincoln Sea, north of Greenland, increased significantly from 2007 to 2010, slightly lagging changes in the eastern and central Arctic. The anomaly was primarily caused by a decrease in the upper ocean salinity. In 2011 upper ocean salinities in the Lincoln Sea returned to values similar to those prior to 2007. Throughout 2008-2010, the freshest surface waters in the western Lincoln Sea show water mass properties similar to fresh Canada Basin waters north of the Canadian Arctic Archipelago. In the northeastern Lincoln Sea fresh surface waters showed a strong link with those observed in the Makarov Basin near the North Pole. The freshening in the Lincoln Sea was associated with a return of a subsurface Pacific Water temperature signal although this was not as strong as observed in the early 1990s. Comparison of repeat stations from the 2000s with the data from the 1990s at 65W showed an increase of the Atlantic temperature maximum which was associated with the arrival of warmer Atlantic water from the Eurasian Basin. Satellite-derived dynamic ocean topography of winter 2009 showed a ridge extending parallel to the Canadian Archipelago shelf as far as the Lincoln Sea, causing a strong flow toward Nares Strait and likely Fram Strait. The total volume of anomalous freshwater observed in the Lincoln Sea and exported by 2011 was close to 1100250km3, approximately 13% of the total estimated FW increase in the Arctic in 2008.

  5. High Biomass Low Export Regimes in the Southern Ocean

    SciTech Connect

    Lam, Phoebe J.; Bishop, James K.B.

    2006-01-27

    This paper investigates ballasting and remineralization controls of carbon sedimentation in the twilight zone (100-1000 m) of the Southern Ocean. Size-fractionated (<1 {micro}m, 1-51 {micro}m, >51 {micro}m) suspended particulate matter was collected by large volume in-situ filtration from the upper 1000 m in the Subantarctic (55 S, 172 W) and Antarctic (66 S, 172 W) zones of the Southern Ocean during the Southern Ocean Iron Experiment (SOFeX) in January-February 2002. Particles were analyzed for major chemical constituents (POC, P, biogenic Si, CaCO3), and digital and SEM image analyses of particles were used to aid in the interpretation of the chemical profiles. Twilight zone waters at 66 S in the Antarctic had a steeper decrease in POC with depth than at 55 S in the Subantarctic, with lower POC concentrations in all size fractions at 66 S than at 55 S, despite up to an order of magnitude higher POC in surface waters at 66 S. The decay length scale of >51 {micro}m POC was significantly shorter in the upper twilight zone at 66 S ({delta}{sub e}=26 m) compared to 55 S ({delta}{sub e}=81 m). Particles in the carbonate-producing 55 S did not have higher excess densities than particles from the diatom-dominated 66 S, indicating that there was no direct ballast effect that accounted for deeper POC penetration at 55 S. An indirect ballast effect due to differences in particle packaging and porosities cannot be ruled out, however, as aggregate porosities were high ({approx}97%) and variable. Image analyses point to the importance of particle loss rates from zooplankton grazing and remineralization as determining factors for the difference in twilight zone POC concentrations at 55 S and 66 S, with stronger and more focused shallow remineralization at 66 S. At 66 S, an abundance of large (several mm long) fecal pellets from the surface to 150 m, and almost total removal of large aggregates by 200 m, reflected the actions of a single or few zooplankton species capable of grazing diatoms in the euphotic zone, coupled with a more diverse particle feeding zooplankton community immediately below. Surface waters with high biomass levels and high proportion of biomass in the large size fraction were associated with low particle loading at depth, with all indications implying conditions of low export. The 66 S region exhibits this 'High Biomass, Low Export' (HBLE) condition, with very high >51 {micro}m POC concentrations at the surface ({approx}2.1 {micro}M POC), but low concentrations below 200 m (<0.07 {micro}M POC). The 66 S region remained HBLE after iron fertilization. Iron addition at 55 S caused a ten fold increase in >51 {micro}m biomass concentrations in the euphotic zone, bringing surface POC concentrations to levels found at 66 S ({approx}3.8 {micro}M), and a concurrent decrease in POC concentrations below 200 m. The 55 S region, which began with moderate levels of biomass and stronger particle export, transitioned to being HBLE after iron fertilization. We propose that iron addition to already HBLE waters will not cause mass sedimentation events. The stability of an iron-induced HBLE condition is unknown. Better understanding of biological pump processes in non-HBLE Subantarctic waters is needed.

  6. 3D Dynamics of Freshwater Lenses in the Near-Surface Layer of the Tropical Ocean

    NASA Astrophysics Data System (ADS)

    Soloviev, Alexander; Dean, Cayla

    2015-04-01

    Convective rains in the Intertropical Convergence Zone (ITCZ) produce lenses of freshened water on the ocean surface. These lenses are localized in space and typically involve both salinity and temperature anomalies. Due to significant density anomalies, strong pressure gradients develop, which result in lateral spreading of freshwater lenses in a form resembling gravity currents. Gravity currents inherently involve three-dimensional dynamics. As a type of organized structure, gravity currents in the upper layer of the ocean may also interact with, and be shaped by, the ambient oceanic environment and atmospheric conditions. Among the important factors are the background stratification, wind stress, wind/wave mixing and spatially coherent organized motions in the near-surface layer of the ocean. Under certain conditions, a resonant interaction between a propagating freshwater lens and internal waves in the underlying pycnocline (e.g., barrier layer) may develop, whereas interaction with wind stress may produce an asymmetry in the freshwater lens and associated mixing. These two types of interactions working in concert may explain the series of sharp frontal interfaces, which have been observed in association with freshwater lenses during TOGA COARE. In this work, we have conducted a series of numerical experiments using computational fluid dynamics tools. These numerical simulations were designed to elucidate the relationship between vertical mixing and horizontal advection of salinity under various environmental conditions and potential impact on the Aquarius and SMOS satellite image formation. Available near-surface data from field experiments served as a guidance for numerical simulations. The results of this study indicate that 3D dynamics of freshwater lenses are essential within a certain range of wind/wave conditions and the freshwater influx in the surface layer of the ocean.

  7. Global Ocean Sensitivity to Local Geologically Short-Term Variability of Freshwater Fluxes

    NASA Astrophysics Data System (ADS)

    Seidov, D.; Haupt, B. J.

    2004-12-01

    The geologic record and computer modeling indicate that the transitions between cold and warm climates during the last deglaciation , driven by internal climate dynamics, were geologically very fast, lasting for only decades or shorter. The THC is, perhaps, the only viable candidate for driving these kinds of abrupt changes. Current perception of how the THC may become an agent of abrupt climate change is that the THC is rather sensitive to changes in freshwater fluxes in the high-latitudes, also known as major meltwater events. Our recent numerical experiments challenge the idea of the high-latitudinal meltwater events as the only possible cause of THC alteration. These experiments suggest that the inter-basin sea surface salinity contrasts caused by disparity of freshwater fluxes over the world ocean can also be a very potent factor in THC dynamics. To address the role of changes in both high-latitudinal and inter-basin freshwater fluxes in altering the global THC, we performed several simple numerical experiments. First, we ran the atmospheric control experiment using the NCAR Community Climate Model (CCM) with observed sea surface temperature (SST) and salinity to get the present-day control atmospheric state, that is, the wind stress, SST, and freshwater fluxes across the sea surfaces. Next, we ran the oceanic control experiment using the GFDL Modular Ocean Model (MOM) with these sea surface conditions from the CCM. In the first series of experiments, we specified idealized anomalies of freshwater fluxes in the northern North Atlantic, the Southern Ocean, and the subtropical North Atlantic and North Pacific. These experiments gave us insight on the relative importance of high-latitudinal and inter-basin short-term fluctuations in freshwater balance for the THC dynamics. In the second series of experiments, we simulated the disruption of the freshwater regime in the northern North Atlantic caused by freshwater floods from Lake Agassiz (a glacial lake that drained into the Hudson Bay around 8.2 kyr BP). The estimates of freshwater discharged into the northern North Atlantic suggest that these volumes of freshwater could be sufficient for large-scale disturbances of the THC. The results of the two series of experiments will be shown and discussed.

  8. Trends in Arctic Ocean bottom pressure, sea surface height and freshwater content using GRACE and the ice-ocean model PIOMAS from 2008-2012

    NASA Astrophysics Data System (ADS)

    Peralta-Ferriz, Cecilia; Morison, James; Zhang, Jinlun; Bonin, Jennifer

    2014-05-01

    The variability of ocean bottom pressure (OBP) in the Arctic is dominated by the variations in sea surface height (SSH) from daily to monthly timescales. Conversely, OBP variability is dominated by the changes in the steric pressure (StP) at inter-annual timescales, particularly off the continental shelves. The combination of GRACE-derived ocean bottom pressure and ICESat altimetry-derived sea surface height variations in the Arctic Ocean have provided new means of identifying inter-annual trends in StP (StP = OBP-SSH) and associated freshwater content (FWC) of the Arctic region (Morison et al., 2012). Morison et al. (2012) showed that from 2004 to 2008, the FWC increased in the Beaufort Gyre and decreased in the Siberian and Central Arctic, resulting in a relatively small net basin-averaged FWC change. In this work, we investigate the inter-annual trends from 2008 to 2012 in OBP from GRACE, SSH from the state-of-the-art pan-Arctic ocean model PIOMAS -validated with tide and pressure gauges in the Arctic-, and compute the trends in StP and FWC from 2008-2012. We compare these results with the previous trends from 2005-2008 described in Morison et al. (2012). Our initial findings suggest increased salinity in the entire Arctic basin (relative to the climatological seasonal variation) from 2008-2012, compared to the preceding four years (2005-2008). We also find that the trends in OBP, SSH and StP from 2008-2012 present a different behavior during the spring-summer and fall-winter, unlike 2005-2008, in which the trends were generally consistent through all months of the year. It seems since 2009, when the Beaufort Gyre relaxed and the export of freshwater from the Canada Basin into the Canadian Archipelago and Fram Strait, via the Lincoln Sea, was anomalously large (de Steur et al., 2013), the Arctic Ocean has entered a new circulation regime. The causes of such changes in the inter-annual trends of OBP, SSH and StP -hence FWC-, associated with the changes in the shape and strength of the Arctic Oscillation (AO) and the wind patterns, as well as with the changes in sea ice conditions will be explored. References: Morison, J., R. Kwok, C. Peralta-Ferriz, M. Alkire, I. Rigor, R. Andersen, and M. Steele, Changing Arctic Ocean Freshwater Pathways Measured With ICESat and GRACE, Nature, 481, 66-70, DOI: 10.1038/nature10705, 2012. de Steur, L., et al. (2013), Hydrographic changes in the Lincoln Sea in the Arctic Ocean with focus on an upper ocean freshwater anomaly between 2007 and 2010, J. Geophys. Res. Oceans, 118, 4699-4715, doi:10.1002/jgrc.20341.

  9. Innate immune responses to gut microbiota differ between oceanic and freshwater threespine stickleback populations

    PubMed Central

    Milligan-Myhre, Kathryn; Small, Clayton M.; Mittge, Erika K.; Agarwal, Meghna; Currey, Mark; Cresko, William A.; Guillemin, Karen

    2016-01-01

    ABSTRACT Animal hosts must co-exist with beneficial microbes while simultaneously being able to mount rapid, non-specific, innate immune responses to pathogenic microbes. How this balance is achieved is not fully understood, and disruption of this relationship can lead to disease. Excessive inflammatory responses to resident microbes are characteristic of certain gastrointestinal pathologies such as inflammatory bowel disease (IBD). The immune dysregulation of IBD has complex genetic underpinnings that cannot be fully recapitulated with single-gene-knockout models. A deeper understanding of the genetic regulation of innate immune responses to resident microbes requires the ability to measure immune responses in the presence and absence of the microbiota using vertebrate models with complex genetic variation. Here, we describe a new gnotobiotic vertebrate model to explore the natural genetic variation that contributes to differences in innate immune responses to microbiota. Threespine stickleback, Gasterosteus aculeatus, has been used to study the developmental genetics of complex traits during the repeated evolution from ancestral oceanic to derived freshwater forms. We established methods to rear germ-free stickleback larvae and gnotobiotic animals monoassociated with single bacterial isolates. We characterized the innate immune response of these fish to resident gut microbes by quantifying the neutrophil cells in conventionally reared monoassociated or germ-free stickleback from both oceanic and freshwater populations grown in a common intermediate salinity environment. We found that oceanic and freshwater fish in the wild and in the laboratory share many intestinal microbial community members. However, oceanic fish mount a strong immune response to residential microbiota, whereas freshwater fish frequently do not. A strong innate immune response was uniformly observed across oceanic families, but this response varied among families of freshwater fish. The gnotobiotic stickleback model that we have developed therefore provides a platform for future studies mapping the natural genetic basis of the variation in immune response to microbes. PMID:26681746

  10. Innate immune responses to gut microbiota differ between oceanic and freshwater threespine stickleback populations.

    PubMed

    Milligan-Myhre, Kathryn; Small, Clayton M; Mittge, Erika K; Agarwal, Meghna; Currey, Mark; Cresko, William A; Guillemin, Karen

    2016-02-01

    Animal hosts must co-exist with beneficial microbes while simultaneously being able to mount rapid, non-specific, innate immune responses to pathogenic microbes. How this balance is achieved is not fully understood, and disruption of this relationship can lead to disease. Excessive inflammatory responses to resident microbes are characteristic of certain gastrointestinal pathologies such as inflammatory bowel disease (IBD). The immune dysregulation of IBD has complex genetic underpinnings that cannot be fully recapitulated with single-gene-knockout models. A deeper understanding of the genetic regulation of innate immune responses to resident microbes requires the ability to measure immune responses in the presence and absence of the microbiota using vertebrate models with complex genetic variation. Here, we describe a new gnotobiotic vertebrate model to explore the natural genetic variation that contributes to differences in innate immune responses to microbiota. Threespine stickleback, Gasterosteus aculeatus, has been used to study the developmental genetics of complex traits during the repeated evolution from ancestral oceanic to derived freshwater forms. We established methods to rear germ-free stickleback larvae and gnotobiotic animals monoassociated with single bacterial isolates. We characterized the innate immune response of these fish to resident gut microbes by quantifying the neutrophil cells in conventionally reared monoassociated or germ-free stickleback from both oceanic and freshwater populations grown in a common intermediate salinity environment. We found that oceanic and freshwater fish in the wild and in the laboratory share many intestinal microbial community members. However, oceanic fish mount a strong immune response to residential microbiota, whereas freshwater fish frequently do not. A strong innate immune response was uniformly observed across oceanic families, but this response varied among families of freshwater fish. The gnotobiotic stickleback model that we have developed therefore provides a platform for future studies mapping the natural genetic basis of the variation in immune response to microbes. PMID:26681746

  11. Iron defecation by sperm whales stimulates carbon export in the Southern Ocean.

    PubMed

    Lavery, Trish J; Roudnew, Ben; Gill, Peter; Seymour, Justin; Seuront, Laurent; Johnson, Genevieve; Mitchell, James G; Smetacek, Victor

    2010-11-22

    The iron-limited Southern Ocean plays an important role in regulating atmospheric CO(2) levels. Marine mammal respiration has been proposed to decrease the efficiency of the Southern Ocean biological pump by returning photosynthetically fixed carbon to the atmosphere. Here, we show that by consuming prey at depth and defecating iron-rich liquid faeces into the photic zone, sperm whales (Physeter macrocephalus) instead stimulate new primary production and carbon export to the deep ocean. We estimate that Southern Ocean sperm whales defecate 50 tonnes of iron into the photic zone each year. Molar ratios of C(export):Fe(added) determined during natural ocean fertilization events are used to estimate the amount of carbon exported to the deep ocean in response to the iron defecated by sperm whales. We find that Southern Ocean sperm whales stimulate the export of 4 10(5) tonnes of carbon per year to the deep ocean and respire only 2 10(5) tonnes of carbon per year. By enhancing new primary production, the populations of 12 000 sperm whales in the Southern Ocean act as a carbon sink, removing 2 10(5) tonnes more carbon from the atmosphere than they add during respiration. The ability of the Southern Ocean to act as a carbon sink may have been diminished by large-scale removal of sperm whales during industrial whaling. PMID:20554546

  12. Coralline algal Barium as indicator for 20th century northwestern North Atlantic surface ocean freshwater variability

    PubMed Central

    Hetzinger, S.; Halfar, J.; Zack, T.; Mecking, J. V.; Kunz, B. E.; Jacob, D. E.; Adey, W. H.

    2013-01-01

    During the past decades climate and freshwater dynamics in the northwestern North Atlantic have undergone major changes. Large-scale freshening episodes, related to polar freshwater pulses, have had a strong influence on ocean variability in this climatically important region. However, little is known about variability before 1950, mainly due to the lack of long-term high-resolution marine proxy archives. Here we present the first multidecadal-length records of annually resolved Ba/Ca variations from Northwest Atlantic coralline algae. We observe positive relationships between algal Ba/Ca ratios from two Newfoundland sites and salinity observations back to 1950. Both records capture episodical multi-year freshening events during the 20th century. Variability in algal Ba/Ca is sensitive to freshwater-induced changes in upper ocean stratification, which affect the transport of cold, Ba-enriched deep waters onto the shelf (highly stratified equals less Ba/Ca). Algal Ba/Ca ratios therefore may serve as a new resource for reconstructing past surface ocean freshwater changes. PMID:23636135

  13. Coralline algal barium as indicator for 20th century northwestern North Atlantic surface ocean freshwater variability.

    PubMed

    Hetzinger, S; Halfar, J; Zack, T; Mecking, J V; Kunz, B E; Jacob, D E; Adey, W H

    2013-01-01

    During the past decades climate and freshwater dynamics in the northwestern North Atlantic have undergone major changes. Large-scale freshening episodes, related to polar freshwater pulses, have had a strong influence on ocean variability in this climatically important region. However, little is known about variability before 1950, mainly due to the lack of long-term high-resolution marine proxy archives. Here we present the first multidecadal-length records of annually resolved Ba/Ca variations from Northwest Atlantic coralline algae. We observe positive relationships between algal Ba/Ca ratios from two Newfoundland sites and salinity observations back to 1950. Both records capture episodical multi-year freshening events during the 20th century. Variability in algal Ba/Ca is sensitive to freshwater-induced changes in upper ocean stratification, which affect the transport of cold, Ba-enriched deep waters onto the shelf (highly stratified equals less Ba/Ca). Algal Ba/Ca ratios therefore may serve as a new resource for reconstructing past surface ocean freshwater changes. PMID:23636135

  14. Sensitivity of the Tropical Pacific Ocean to Precipitation Induced Freshwater Flux

    NASA Technical Reports Server (NTRS)

    Yang, Song; Lau, K.-M.; Schopf, Paul S.

    1999-01-01

    We have performed a series of experiments using an ocean model to study the sensitivity of tropical Pacific Ocean to variations in precipitation induced freshwater fluxes. Variations in these fluxes arise from natural causes on all time scales. In addition, estimates of these fluxes are uncertain because of differences among measurement techniques. The model used is a quasi-isopycnal model, covering the Pacific from 40 S to 40 N. The surface forcing is constructed from observed wind stress, evaporation, precipitation, and surface temperature (SST) fields. The heat flux is produced with an iterative technique so as to maintain the model close to the observed climatology, but with only a weak damping to that climatology. Climatological estimates of evaporation are combined with various estimates of precipitation to determine the net surface freshwater flux. Results indicate that increased freshwater input decreases salinity as expected, but increases temperatures in the upper ocean. Using the freshwater flux estimated from the Microwave Sounding Unit leads to a warming of up to 0.6 C in the western Pacific over a case with zero net freshwater flux. SST is sensitive to the discrepancies among different precipitation observations, with root-mean-square differences in SST on the order of 0.2-0.3 C. The change in SST is more pronounced in the eastern Pacific, with differences of over 1 C found among the various precipitation products. Interannual variation in precipitation during El Nino events leads to increased warming. During the winter of 1982-83, freshwater flux accounts for about 0.4 C (approximately 10-15% of the maximum warming) of the surface warming in the central-eastern Pacific. Thus, the error of SST caused by the discrepancies in precipitation products is more than half of the SST anomaly produced by the interannual variability of observed precipitation. Further experiments, in which freshwater flux anomalies are imposed in the western, central, and eastern Pacific, show that the influence of net freshwater flux is also spatially dependent. The imposition of freshwater flux in the far western Pacific leads to a trapping of salinity anomaly to the surface layers near the equator. An identical flux imposed in the central Pacific produces deeper and off-equatorial salinity anomalies. The contrast between these two simulations is consistent with other simulations of the western Pacific barrier layer information.

  15. Effects of freshwater inflow to the ocean on climate simulation using the coupled climate model

    NASA Astrophysics Data System (ADS)

    Ham, S.; Hong, S.-Y.

    2012-04-01

    Freshwater flux has a direct effect on salinity in the ocean, which affects climate and water cycles. It modifies the density of water, mixed layer depth, and mixing and entrainment, all of which can affect sea surface temperature. Moreover, freshwater flux is an important component forcing source driving thermohaline circulation. Recently, the climate modeling community has found the importance of freshwater forcing from precipitation of river to track the flow of water to the ocean on a global scale. However, there are only a few modeling studies considering freshwater forcing and its salinity-related effects on climate variability. In this study the effects of river discharge are investigated on simulated climatology using the coupled model. Two experiments are designed with and without the TRIP, that is, a river routing algorithm. In the run with the TRIP, the salinity is largely decreased, in particular, over the eastern and western Pacific coastal regions. The increase in SST is distinct over the eastern equatorial Pacific region. As a result, the surface fluxes are increased over the eastern Pacific, which enhances precipitation activity. The increase of precipitation over the eastern Pacific and a reduction of it over the north of the equator in the central Pacific, and the southern displacement of tropical rain over the Atlantic oceans improve the precipitation climatology. An overall increase of precipitation activity over the tropics reduces the biases in the large-scale features by warming and moistening the troposphere when the river flow routing is executed. Our results suggest that the inclusion of freshwater routing from the continents to oceans should not be ignored in climate simulation since it alters the SST, which is the external boundary condition for the atmospheric model. This study will be extended to investigate the effects of snow-melting into the coupled model with TRIP.

  16. Where is mineral ballast important for surface export of particulate organic carbon in the ocean?

    PubMed Central

    Le Moigne, Frdric A C; Pabortsava, Katsiaryna; Marcinko, Charlotte L J; Martin, Patrick; Sanders, Richard J

    2014-01-01

    Correlations between particulate organic carbon (POC) and mineral fluxes in the deep ocean have inspired the inclusion of ballast effect parameterizations in carbon cycle models. A recent study demonstrated regional variability in the effect of ballast minerals on the flux of POC in the deep ocean. We have undertaken a similar analysis of shallow export data from the Arctic, Atlantic, and Southern Oceans. Mineral ballasting is of greatest importance in the high-latitude North Atlantic, where 60% of the POC flux is associated with ballast minerals. This fraction drops to around 40% in the Southern Ocean. The remainder of the export flux is not associated with minerals, and this unballasted fraction thus often dominates the export flux. The proportion of mineral-associated POC flux often scales with regional variation in export efficiency (the proportion of primary production that is exported). However, local discrepancies suggest that regional differences in ecology also impact the magnitude of surface export. We propose that POC export will not respond equally across all high-latitude regions to possible future changes in ballast availability. PMID:26074644

  17. Global assessment of ocean carbon export by combining satellite observations and food-web models

    NASA Astrophysics Data System (ADS)

    Siegel, D. A.; Buesseler, K. O.; Doney, S. C.; Sailley, S. F.; Behrenfeld, M. J.; Boyd, P. W.

    2014-03-01

    The export of organic carbon from the surface ocean by sinking particles is an important, yet highly uncertain, component of the global carbon cycle. Here we introduce a mechanistic assessment of the global ocean carbon export using satellite observations, including determinations of net primary production and the slope of the particle size spectrum, to drive a food-web model that estimates the production of sinking zooplankton feces and algal aggregates comprising the sinking particle flux at the base of the euphotic zone. The synthesis of observations and models reveals fundamentally different and ecologically consistent regional-scale patterns in export and export efficiency not found in previous global carbon export assessments. The model reproduces regional-scale particle export field observations and predicts a climatological mean global carbon export from the euphotic zone of ~6 Pg C yr-1. Global export estimates show small variation (typically < 10%) to factor of 2 changes in model parameter values. The model is also robust to the choices of the satellite data products used and enables interannual changes to be quantified. The present synthesis of observations and models provides a path for quantifying the ocean's biological pump.

  18. Ocean export production and foraminiferal stable isotopes in the Antarctic Southern Ocean across the mid-Pleistocene transition

    NASA Astrophysics Data System (ADS)

    Hasenfratz, A. P.; Martinez-Garcia, A.; Jaccard, S.; Hodell, D. A.; Vance, D.; Bernasconi, S. M.; Greaves, M.; Haug, G. H.

    2014-12-01

    Changes in buoyancy forcing in the Antarctic Zone (AZ) of the Southern Ocean are believed to play an instrumental role in modulating atmospheric CO2 concentrations during glacial cycles by regulating the transfer of carbon between the ocean interior and the atmosphere. Indeed, a million-year-spanning high-resolution excess Barium record from the AZ of the South Atlantic (ODP 1094), which traces changes in export production, shows decreased export production during cold periods suggesting decreased overturning. Here, we extend this AZ export production record back to 1.6 Myr. In addition, we present new carbon and oxygen isotope records of benthic and planktic foraminifera from the same site, complemented by Mg/Ca measurements in some intervals. The interpretation of these new data in the context of other South Atlantic records contributes to a better understanding of Southern Ocean hydrography and its role in modulating glacial/interglacial cycles over the past 1.6 Myr.

  19. A change in the freshwater balance of the Atlantic Ocean over the past four decades.

    PubMed

    Curry, Ruth; Dickson, Bob; Yashayaev, Igor

    2003-12-18

    The oceans are a global reservoir and redistribution agent for several important constituents of the Earth's climate system, among them heat, fresh water and carbon dioxide. Whereas these constituents are actively exchanged with the atmosphere, salt is a component that is approximately conserved in the ocean. The distribution of salinity in the ocean is widely measured, and can therefore be used to diagnose rates of surface freshwater fluxes, freshwater transport and local ocean mixing--important components of climate dynamics. Here we present a comparison of salinities on a long transect (50 degrees S to 60 degrees N) through the western basins of the Atlantic Ocean between the 1950s and the 1990s. We find systematic freshening at both poleward ends contrasted with large increases of salinity pervading the upper water column at low latitudes. Our results extend a growing body of evidence indicating that shifts in the oceanic distribution of fresh and saline waters are occurring worldwide in ways that suggest links to global warming and possible changes in the hydrologic cycle of the Earth. PMID:14685235

  20. Export of dissolved inorganic nutrients to the northern Indian Ocean from the Indian monsoonal rivers during discharge period

    NASA Astrophysics Data System (ADS)

    Krishna, M. S.; Prasad, M. H. K.; Rao, D. B.; Viswanadham, R.; Sarma, V. V. S. S.; Reddy, N. P. C.

    2016-01-01

    Coastal regions are highly productive due to the nutrients largely supplied by rivers. To examine the contribution of dissolved inorganic nutrients (DIN) by Indian rivers to coastal waters, data were collected near the freshwater heads of 27 monsoonal rivers of peninsular India during three weeks in late July to mid-August, the middle of the principal runoff period of the southwest monsoon of 2011. Twelve researchers in four groups, equipped with car and portable laboratory equipment, sampled mid-stream of each estuary using mechanized boat, and filtered and partly analyzed the water in the evening. The estimated exports were 0.22 ± 0.05, 0.11 ± 0.03, and 1.03 ± 0.26 Tg yr-1 for dissolved inorganic nitrogen, phosphorus and silicate, respectively. Higher amounts of DIN reach the Bay of Bengal than the Arabian Sea due to the higher volume (∼76%) of discharge to the former. In contrast, the export of dissolved inorganic nitrogen is almost same to the Bay of Bengal (0.12 ± 0.03 Tg yr-1) and Arabian Sea (0.10 ± 0.02 Tg yr-1) principally due to the polluted Narmada and Tapti rivers in the northwest. Including input from the glacial rivers, Ganges, Brahmaputra and Indus, it is estimated that the northern Indian Ocean receives ∼1.84 ± 0.46, 0.28 ± 0.07 and 3.58 ± 0.89 Tg yr-1 of nitrate, phosphate and silicate, respectively, which are significantly lower than the earlier estimates of DIN export from the Indian rivers based on DIN measured in the mid or upstream rivers. Such low fluxes in this study were attributed to efficient retention/elimination of DIN (∼91%) before reaching the coastal ocean. Hence, this study suggests that the importance of sampling locations for estimating nutrient fluxes to the coastal ocean. Riverine DIN export of 1.84 ± 0.46 Tg yr-1 would support 12.2 ± 3.1 Tg C yr-1 of new production in coastal waters of the northern Indian Ocean that results in a removal of 12.2 ± 3.1 Tg atmospheric CO2 yr-1.

  1. Export Production in the Southern Ocean Estimated from Satellite Ocean Color Data and Seasonal Variations in Atmospheric Potential Oxygen

    NASA Astrophysics Data System (ADS)

    Nevison, C. D.; Keeling, R. F.; Kahru, M.; Manizza, M.; Charette, M. A.; Maiti, K.

    2010-12-01

    A quantitative estimate of export production is important for understanding the global carbon cycle and the role of the oceanic biological pump in sequestering anthropogenic carbon dioxide. In the important Southern Ocean region, export production takes place predominantly during the spring and summer. Since each mole of photosynthetically-fixed carbon that is exported from the mixed layer leaves behind a stoichiometric amount of oxygen, which is available for release to the atmosphere, it has long been hypothesized that seasonal variations in Atmospheric Potential Oxygen (APO ~ O2/N2 + 1.1 CO2) can be used to constrain oceanic Net Community Production (NCP), which approximately balances export production in a steady-state system. However, the seasonal cycle of APO reflects three seasonally-varying ocean processes: NCP, deep water ventilation and thermal in and outgassing, and one must account for the two latter terms in order to estimate the signal in APO data due to NCP. This study attempts to resolve the three components of the APO seasonal cycle using a variety of independent approaches: 1) estimating the ventilation signal based on atmospheric nitrous oxide data and inferring the production signal as a residual, 2) estimating the production signal based on satellite ocean color data and inferring the ventilation signal as a residual, 3) decomposing the oxygen cycle using an ocean general circulation biogeochemistry model. Method 2 unavoidably requires the intervention of an atmospheric transport model, which introduces substantial uncertainties, to translate satellite-based sea-to-air fluxes into an atmospheric signal. In contrast, Method 1 in principle can be based entirely on atmospheric data, if a new method involving the atmospheric argon/nitrogen ratio is used to estimate the thermal signal in APO. However, uncertainties in the auxiliary atmospheric data, including nitrous oxide and argon, limit confidence in Method 1 at present. Within the uncertainties, all three methods converge on a similar solution when applied to Southern Ocean APO data. This convergence advances our understanding of the APO seasonal cycle and its component signals. In particular, our results suggest that a) APO data, while confirming that current satellite ocean color-based estimates of Southern Ocean export flux are reasonable in phase and amplitude, cannot at present provide a strong quantitative constraint on these estimates, and b) APO data, corrected for thermal signals, provide a reasonable estimate of the seasonal signal of deep ventilation from the critical Southern Ocean region, after subtracting a production signal estimated from satellite ocean color data.

  2. Coastal Downscaling Experiments: Can CESM Fields Successfully Force Regional Coastal Ocean Simulations with Strong Freshwater Forcing?

    NASA Astrophysics Data System (ADS)

    MacCready, P.; Bryan, F.; Tseng, Y. H.; Whitney, M. M.

    2014-12-01

    The coastal ocean accounts for about half of the global fish harvest, but is poorly resolved in global climate models (a one-degree grid barely sees the continental shelf). Moreover, coastal ocean circulation is strongly modified by river freshwater sources, often coming from estuarine systems that are completely unresolved in the coarse grid. River freshwater input in CESM is added in a practical but ad hoc way, by imposing a surface salinity sink over a region of the ocean approximating the plume area of a given river. Here we present results from a series of model experiments using a high-resolution (1.5 km) ROMS model of the NE Pacific, including the Columbia River and the inland waters of Puget Sound. The base model does multi-year hindcasts using the best available sources of atmospheric (MM5/WRF), ocean (NCOM), river (USGS), and tidal forcing. It has been heavily validated against observations of all sorts, and performs well, so it is an ideal test bed for downscaling experiments. The model framework also does biogeochemistry, including oxygen, and carbon chemistry is being added to make forecasts of Ocean Acidification.This high-resolution ROMS model is systematically run in downscaling experiments for the year 2005 with combinations of CESM forcing (CAM, POP, and rivers) swapped in. Skill is calculated using observations. It is found that the runs with CESM forcing generally retain much of the skill of the base model. A compact metric of response to freshwater forcing is used, which is the mechanical energy required to destratify a shallow coastal volume. This, along with the average temperature and salinity of the volume, are used to characterize and compare runs, including the original CESM-POP fields. Finally the model is run with projected CESM simulation forcing at the end of 21st century based on a set of RCP scenarios, and the compact metrics are used to quantify differences from 2005.

  3. Quantifying export production in the Southern Ocean: Implications for the Baxs proxy

    NASA Astrophysics Data System (ADS)

    Hernandez-Sanchez, Maria T.; Mills, Rachel A.; Planquette, HLNe; Pancost, Richard D.; Hepburn, Laura; Salter, Ian; Fitzgeorge-Balfour, Tania

    2011-12-01

    The water column and sedimentary Baxs distribution around the Crozet Plateau is used to decipher the controls and timing of barite formation and to evaluate how export production signals are recorded in sediments underlying a region of natural Fe fertilization within the Fe limited Southern Ocean. Export production estimated from preserved, vertical sedimentary Baxs accumulation rates are compared with published export fluxes assessed from an integrated study of the biological carbon pump to determine the validity of Baxs as a quantitative proxy under different Fe supply conditions typical of the Southern Ocean. Detailed assessment of the geochemical partitioning of Ba in sediments and the lithogenic end-member allows appropriate correction of the bulk Ba content and determination of the Baxs content of sediments and suspended particles. The upper water column distribution of Baxs is extremely heterogeneous spatially and temporally. Organic carbon/Baxs ratios in deep traps from the Fe fertilized region are similar to other oceanic settings allowing quantification of the inferred carbon export based on established algorithms. There appears to be some decoupling of POC and Ba export in the Fe limited region south of the Plateau. The export production across the Crozet Plateau inferred from the Baxs sedimentary proxy indicates that the Fe fertilized area to the north of the Plateau experiences enhanced export relative to equivalent Southern Ocean settings throughout the Holocene and that this influence may also have impacted the site to the south for significant periods. This interpretation is corroborated by alternative productivity proxies (opal accumulation, 231Paxs/230Thxs). Baxs can be used to quantify export production in complex settings such as naturally Fe-fertilized (volcanoclastic) areas, providing appropriate lithogenic correction is undertaken, and sediment focusing is corrected for along with evaluation of barite preservation.

  4. Mercury export to the Arctic Ocean from the Mackenzie River, Canada.

    PubMed

    Emmerton, Craig A; Graydon, Jennifer A; Gareis, Jolie A L; St Louis, Vincent L; Lesack, Lance F W; Banack, Janelle K A; Hicks, Faye; Nafziger, Jennifer

    2013-07-16

    Circumpolar rivers, including the Mackenzie River in Canada, are sources of the contaminant mercury (Hg) to the Arctic Ocean, but few Hg export studies exist for these rivers. During the 2007-2010 freshet and open water seasons, we collected river water upstream and downstream of the Mackenzie River delta to quantify total mercury (THg) and methylmercury (MeHg) concentrations and export. Upstream of the delta, flow-weighted mean concentrations of bulk THg and MeHg were 14.6 ± 6.2 ng L(-1) and 0.081 ± 0.045 ng L(-1), respectively. Only 11-13% and 44-51% of bulk THg and MeHg export was in the dissolved form. Using concentration-discharge relationships, we calculated bulk THg and MeHg export into the delta of 2300-4200 kg yr(-1) and 15-23 kg yr(-1) over the course of the study. Discharge is not presently known in channels exiting the delta, so we assessed differences in river Hg concentrations upstream and downstream of the delta to estimate its influence on Hg export to the ocean. Bulk THg and MeHg concentrations decreased 19% and 11% through the delta, likely because of particle settling and other processes in the floodplain. These results suggest that northern deltas may be important accumulators of river Hg in their floodplains before export to the Arctic Ocean. PMID:23800098

  5. Carbon export and transfer to depth across the Southern Ocean Great Calcite Belt

    NASA Astrophysics Data System (ADS)

    Rosengard, S. Z.; Lam, P. J.; Balch, W. M.; Auro, M. E.; Pike, S.; Drapeau, D.; Bowler, B.

    2015-07-01

    Sequestration of carbon by the marine biological pump depends on the processes that alter, remineralize, and preserve particulate organic carbon (POC) during transit to the deep ocean. Here, we present data collected from the Great Calcite Belt, a calcite-rich band across the Southern Ocean surface, to compare the transformation of POC in the euphotic and mesopelagic zones of the water column. The 234Th-derived export fluxes and size-fractionated concentrations of POC, particulate inorganic carbon (PIC), and biogenic silica (BSi) were measured from the upper 1000 m of 27 stations across the Atlantic and Indian sectors of the Great Calcite Belt. POC export out of the euphotic zone was correlated with BSi export. PIC export was not, but did correlate positively with POC flux transfer efficiency. Moreover, regions of high BSi concentrations, which corresponded to regions with proportionally larger particles, exhibited higher attenuation of > 51 μm POC concentrations in the mesopelagic zone. The interplay among POC size partitioning, mineral composition, and POC attenuation suggests a more fundamental driver of POC transfer through both depth regimes in the Great Calcite Belt. In particular, we argue that diatom-rich communities produce large and labile POC aggregates, which not only generate high export fluxes but also drive more remineralization in the mesopelagic zone. We observe the opposite in communities with smaller calcifying phytoplankton, such as coccolithophores. We hypothesize that these differences are influenced by inherent differences in the lability of POC exported by different phytoplankton communities.

  6. Carbon export and transfer to depth across the Southern Ocean Great Calcite Belt

    NASA Astrophysics Data System (ADS)

    Rosengard, S. Z.; Lam, P. J.; Balch, W. M.; Auro, M. E.; Pike, S.; Drapeau, D.; Bowler, B.

    2015-02-01

    Sequestration of carbon by the marine biological pump depends on the processes that alter, remineralize and preserve particulate organic carbon (POC) during transit to the deep ocean. Here, we present data collected from the Great Calcite Belt, a calcite-rich band across the Southern Ocean surface, to compare the transformation of POC in the euphotic and mesopelagic zones of the water column. The 234Th-derived export fluxes and size-fractionated concentrations of POC, particulate inorganic carbon (PIC), and biogenic silica (BSi) were measured from the upper 1000 m of 27 stations across the Atlantic and Indian sectors of the Great Calcite Belt. POC export out of the euphotic zone was correlated with BSi export. PIC export was not, but did correlate positively with POC flux transfer efficiency. Moreover, regions of high BSi concentrations, which corresponded to regions with proportionally larger particles, exhibited higher attenuation of >51 μm POC concentrations in the mesopelagic zone. The interplay among POC size partitioning, mineral composition and POC attenuation suggests a more fundamental driver of POC transfer through both depth regimes in the Great Calcite Belt. In particular, we argue that diatom-dominated communities produce large and labile POC aggregates, which generate high export fluxes but also drive more remineralization in the mesopelagic zone. We observe the opposite in communities with smaller calcifying phytoplankton, such as coccolithophores. We hypothesize that these differences are influenced by inherent differences in the lability of POC exported by different phytoplankton communities.

  7. Large Freshwater Anomalies in the Arctic Ocean: Results from the 2008 IPY/NPEO Hydrographic Survey

    NASA Astrophysics Data System (ADS)

    McPhee, M.; Morison, J.; Proshutinsky, A.; Steele, M.

    2008-12-01

    Based on an aerial hydrographic survey conducted in March and April, 2008, supplemented by unmanned drifting ice-tethered profilers (ITPs), we report that the precipitous decrease in minimum Arctic ice extent observed in the past few years has been accompanied by significant changes in upper ocean salinity, especially over the Canada Basin, where the anticyclonic Beaufort Gyre has traditionally maintained one of the major freshwater reservoirs of the world ocean. Our winter measurements corroborate and extend observations of increased summer freshwater content (FWC) first detected during the joint WHOI-IOS- JAMSTEC expedition in 2003 and monitored since. The survey comprised operations in the western Arctic that included 15 ice-landing stations and 8 airdropped expendable probes, plus 20 ice-landing stations in the eastern Arctic staged from ice station Barneo near the North Pole. We found that in the southeast quadrant of the Canada Basin, anomalous FWC (i.e., the change relative to PHC 3.0 winter [March-April-May] climatology based predominantly on conditions in the 1970s) has increased by as much as 11 m. Positive anomalies were found at all stations in the Pacific sector, including ITP profiles, but their magnitudes decreased to the west and north. In the eastern Arctic we found negative FWC anomalies on the Eurasian side of the Lomonosov Ridge, reaching values as low as -5 m. Smaller positive anomalies characterized water in the Makarov Basin. Freshening of the upper ocean over the Canada Basin has also substantially changed steric levels. A west- to-east line of stations extending about 800 km across the Basin, centered near 75N, 150W, nearly bisected the traditional Beaufort Gyre. In contrast to the domed climatological dynamic topography typical of the Gyre, the 2008 survey showed a monotonic rise in dynamic height as far east as 135W, indicating a northward surface geostrophic flow component across the entire section, with large impact on freshwater transport.

  8. The Arctic Mediterranean Sea - Deep convection, oceanic heat transport and freshwater

    NASA Astrophysics Data System (ADS)

    Rudels, Bert

    2014-05-01

    The speculations about the driving forces behind the oceanic meridional circulation and the importance of the northward transports of oceanic heat for the ice conditions in the Arctic Ocean have a long history, but only after the Fram expedition 1893-1896 and from the studies by Nansen, Helland-Hansen and Sandstrm in the early 1900s did these speculations attain observational substance. In the late 1970s and onward these questions have again risen to prominence. A study of deep convection in the Greenland Sea, then assumed to drive the global thermohaline circulation, started with the Greenland Sea Project (GSP), while the investigation of the exchanges of volume and heat through Fram Strait had a more hesitant start in the Fram Strait Project (FSP). Not until 1997 with the EC project VEINS (Variation of Exchanges in the Northern Seas) was a mooring array deployed across Fram Strait. This array has been maintained and has measured the exchanges ever since. Eberhard Fahrbach was closely involved in these studies, as a secretary for the GSP and as the major driving force behind the Fram Strait array. Here we shall examine the legacy of these projects; How our understanding of these themes has evolved in recent years. After the 1980s no convective bottom water renewal has been observed in the Greenland Sea, and the Greenland Sea deep waters have gradually been replaced by warmer, more saline deep water from the Arctic Ocean passing through Fram Strait. Small-scale convective events penetrating deeper than 2500m but there less dense than their surroundings were, however, observed in the early 2000s. The Fram Strait exchanges have proven difficult to estimate due to strong variability, high barotropic and baroclinic eddy activity and short lateral coherence scales. The fact that the mass transports through Fram Strait do not balance complicates the assessment of the heat transport through Fram Strait into the Arctic Ocean and mass (volume) and salt (freshwater) balances for the entire Arctic Ocean are needed. The waters exiting the Arctic Ocean through Fram Strait are colder than those entering and with reasonable assumptions about the origin of the waters providing the net outflow it is possible to deduce the amount of the entering oceanic heat going to the atmosphere (>50%), to ice melt (20%). Almost all of this heat loss occurs in the Nansen Basin. The rest of the heat is used for heating the net outflow. It also becomes clear that freshwater, with its phase changes and its multiple transport pathways, plays a crucial role in the climate, not just of the Arctic Ocean but of the Arctic as a whole.

  9. Modeling dissolved organic carbon and carbon export in the equatorial Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Liu, Na; Zeng, Lili; Li, Yizhen; Xiu, Peng

    2015-04-01

    The newly built CoSiNE-31 ecosystem model developed for the Pacific Ocean is employed here to evaluate carbon cycling in the equatorial Pacific upwelling region. This model explicitly includes 31 state variables capable of reproducing key biogeochemical features in this region, such as high-nutrient low-chlorophyll conditions. In the so-called Wyrtki Box (5S-5N, 90-180W), the modeled area-averaged carbon export data show the predominance of the particulate organic carbon flux. This is consistent with observations, and amounts to 7.88 mmol C m-2 day-1 at the bottom of the euphotic zone (120 m water depth). Nearly as important is the dissolved organic carbon export flux, at 6.62 mmol C m-2 day-1. The modeled particulate inorganic carbon (PIC) export flux of 2.07 mmol C m-2 day-1 is much higher than the global average, indicating a key role of PIC sedimentation in the study region. The modeled carbon-to-nitrogen export ratio for particulate organic matter (POM) is 7.8, which is consistent with the Redfield ratio. The export ratio increases to 13.8 for dissolved organic matter (DOM). By implication, carbon export is markedly more efficient via DOM than via POM. This is the case also under simulated iron enrichment conditions, although there are measurable increases in carbon export efficiency for both DOM and POM.

  10. Carbon export mediated by mesopelagic fishes in the northeast Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Davison, P. C.; Checkley, D. M.; Koslow, J. A.; Barlow, J.

    2013-09-01

    The role of fishes in the global carbon cycle is poorly known and often neglected. We show that the biomass of mesopelagic fishes off the continental USA west to longitude 141°W is positively related to annual net primary productivity, and averages 17 g m-2. We estimate the export of carbon out of the epipelagic ocean mediated by mesopelagic fishes (“fish-mediated export”; FME) with individual-based metabolic modeling using the catch from 77 mesopelagic trawls distributed over the study area. FME was 15-17% (22-24 mg C m-2 d-1) of the total carbon exported in the study area (144 mg C m-2 d-1), as estimated from satellite data. FME varies spatially in both magnitude and relative importance. Although the magnitude of FME increases with increasing total export, the ratio of FME to total export decreases. FME exceeds 40% of the total carbon export in the oligotrophic North Pacific Subtropical Gyre, but forms <10% of the total export in the most productive waters of the California Current. Because the daytime residence depth of these fishes is below the depths where most remineralization of sinking particles occurs, FME is approximately equal to the passive transport at a depth of 400 m. The active transport of carbon by mesopelagic fishes and zooplankton is similar in magnitude to the gap between estimates of carbon export obtained with sediment traps and by other methods. FME should be considered in models of the global carbon cycle.

  11. Strong hemispheric coupling of glacial climate through freshwater discharge and ocean circulation.

    PubMed

    Knutti, R; Flückiger, J; Stocker, T F; Timmermann, A

    2004-08-19

    The climate of the last glacial period was extremely variable, characterized by abrupt warming events in the Northern Hemisphere, accompanied by slower temperature changes in Antarctica and variations of global sea level. It is generally accepted that this millennial-scale climate variability was caused by abrupt changes in the ocean thermohaline circulation. Here we use a coupled ocean-atmosphere-sea ice model to show that freshwater discharge into the North Atlantic Ocean, in addition to a reduction of the thermohaline circulation, has a direct effect on Southern Ocean temperature. The related anomalous oceanic southward heat transport arises from a zonal density gradient in the subtropical North Atlantic caused by a fast wave-adjustment process. We present an extended and quantitative bipolar seesaw concept that explains the timing and amplitude of Greenland and Antarctic temperature changes, the slow changes in Antarctic temperature and its similarity to sea level, as well as a possible time lag of sea level with respect to Antarctic temperature during Marine Isotope Stage 3. PMID:15318212

  12. The competition of freshwater and radiation in forcing the ocean during El Nino

    SciTech Connect

    Schneider, N.; Barnett, T.P.

    1995-05-01

    The relative roles of heat and freshwater fluxes in forcing the tropical Pacific on interannual timescales are investigated using sophisticated atmospheric and oceanic general circulation models. Interannual density flux anomalies due to anomalous precipitation and shortwave and longwave radiation are highly correlated since they all depend on clouds. Their respective contributions to the anomalous surface density flux are of comparable magnitude, with precipitation and longwave anomalies opposing shortwave radiation. This implies that anomalous radiation and precipitation associated with the eastward shift of the centers of deep convection during El Nino change the density flux little since they largely balance. This near cancellation also causes the evaporative component to dominate interannual anomalies of the density flux in the eastern Pacific and in the Indian Ocean and implies that anomalous net surface density fluxes there can be approximated by anomalous evaporation alone. However, in the central and western Pacific, evaporative anomalies are negatively correlated to shortwave anomalies as well, and interannual anomalies of the net density flux are therefore small and deviate considerable from the evaporative component alone. Forcing an oceanic circulation model with the interannual anomalies of the fluxes of heat and freshwater alone yields salinity and temperature anomalies of the same order as observed. Model salinity anomalies explain approximately half of the observations, while temperature anomalies have reversed signs compared to observations. This reflects the negative feedback between surface heat fluxes and the warming caused by interannual anomalies of the wind not included in this simulation. Over most of the tropical ocean, interannual anomalies of surface density are dominated by temperature anomalies. In the central Pacific salinity anomalies diminish up to half of the effect of temperature. 28 refs., 18 figs., 1 tab.

  13. 234Th-derived particulate organic carbon export flux in the western Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Yu, Wen; Chen, Liqi; Cheng, Jianping; He, Jianhua; Yin, Mingduan; Zeng, Zhi

    2010-11-01

    To evaluate the particle dynamics and estimate the POC (particulate organic carbon) export flux from the euphotic zone in the western Arctic Ocean, 234Th-238U disequilibrium was applied during the second Chinese National Arctic Research Expedition (July 15-September 26, 2003). The POC export fluxes are estimated from the measured profiles of the 234Th/238U activity ratios and the POC/PTh ratios. The average residence times of the particulate and dissolved 234Th in the euphotic zone are 33 d and 121 d, and their average export fluxes are 480 dpm/m2d and 760 dpm/m2d, respectively. The scavenging and removal processes of particle reactive elements are active in the upper layer of the Chukchi Sea. The average residence time of 234Th increases from shelf to basin, while the export fluxes of 234Th decrease. The estimated POC export fluxes from the euphotic zone vary from 2.1 to 20.3 mmol/m2d, indicating that the western Arctic Ocean is an important carbon sink in summer due to efficient biological pump.

  14. Southern Ocean overturning, export production and climate variability over the past 1 Myr

    NASA Astrophysics Data System (ADS)

    Jaccard, S.; Hayes, C. T.; Martinez Garcia, A.; Galbraith, E. D.; Anderson, R. F.; Sigman, D. M.; Haug, G. H.

    2011-12-01

    Recently developed XRF core-scanning methods permit paleoceanographic reconstructions on time-scales similar to ice core temperature and atmospheric carbon dioxide measurements. We have investigated distribution of carbonate and biogenic barium (bioBa) - a proxy for integrated organic carbon export - in a sedimentary archive retrieved from the deep South Atlantic (ODP 1094, 53S, 6E, 2807 m) covering the past 1 Myr. These measurements are complemented with high-resolution, 230Th-normalized opal, bioBa and chlorin flux determinations spanning the last 150 kyrs. Our multi-proxy approach reveals that export production and biogenic carbonate preservation were tightly linked to atmospheric pCO2 reconstructions over the last 1 Myr. In particular, lukewarm interglacials (i.e. MIS 13-19) show generally lower organic matter export and reduced carbonate preservation when compared to more recent interglacials. This supports the critical contribution of Southern Ocean deglacial upwelling to modulate the partitioning of CO2 between the ocean interior and the atmosphere over the last million years, and immediately suggests that the moderate pCO2 increases during the lukewarm interglacials were due to a reduced dynamic range of Southern Ocean overturning. Changes in the vertical structure of the Southern Ocean water-column do not only prove to be crucial for the transitions from glacial to interglacial climate states. The decrease in upwelling following peak interglacial conditions leads the climate system to progressively converge towards colder, glacial conditions. Once a pCO2 threshold value of about 225 ppmv is reached, export production tends to stabilize around very low values, consistent with more strongly stratified conditions. This threshold also marks the abrupt inception of iron-rich mineral dust generation and deposition downwind of major South American dust sources, thereby catalyzing export production in the Subantarctic Zone of the Southern Ocean, to the north of ODP site 1094. New evidence from ODP site 1090 (42S, 9E, 3700 m) shows that iron fertilization in the SAZ would have permitted to sequester additional remineralized carbon in the ocean interior, forcing the climate system to reach full glacial conditions. This mechanism was only effective when the Southern Ocean lid was already sealed, precluding the sequestered CO2 to evade through the Antarctic valve. The threshold persisted throughout the lukewarm interval, suggesting that processes taking place in the Antarctic Zone of the Southern Ocean were responsible for the observed reduced interglacial pCO2 levels.

  15. Strengths and weaknesses of the global ocean conveyor: Inter-basin freshwater disparities as the major control

    NASA Astrophysics Data System (ADS)

    Haupt, Bernd J.; Seidov, Dan

    2007-05-01

    According to the current paradigm of modern climatology and oceanography, the global ocean thermohaline circulation works as the so-called global ocean salinity conveyor belt - a system of currents connecting different ocean basins and most notably - the northern North Atlantic and northern North Pacific Oceans - the most distant regions of the world ocean. It is shown here that a slight disparity in freshwater redistribution between the Atlantic and Pacific oceans can be sufficient for building up and maintaining a global conveyor-type ocean thermohaline circulation. On the other hand, relatively small changes in this disparity leading to change in sea surface salinity contrasts between and in the north-south within the northern parts of these two oceans can easily change the conveyor.

  16. Seasonal Variation, Export Dynamics and Consumption of Freshwater Invertebrates in an Estuarine Environment

    NASA Astrophysics Data System (ADS)

    Williams, D. D.; Williams, N. E.

    1998-03-01

    In the Aber Estuary, North Wales, significant numbers of freshwater benthic invertebrates occurred in the tidal freshwater area. Distinct seasonal patterns were observed in their longitudinal zonation which appeared to be unrelated to variations in tidal inundation. The December extension downstream of freshwater taxa is hypothesized to be in response to decreasing water temperatures. In April, larvae/nymphs of the Trichoptera (caddisflies), Ephemeroptera (mayflies) and Plecoptera (stoneflies) ranged as far as a site inundated by 80·9% of all high tides, and larval Elmidae and Chironomidae (midges) occurred at the most marine site (inundated twice daily by all high tides). In July, with the exception of the Chironomidae, the range of most aquatic insects had contracted to the upper estuary. Although, in general, densities of aquatic insects decreased towards the lower estuary, significant densities persisted there. For example, maxima of 3514 chironomid larvae and 48 caddisfly larvae m -2were recorded at the 80·9% inundation site. An estimated 31×10 6freshwater invertebrates (weighing 62·6 kg), per annum, passed from fresh water into salt water across any given transect along the estuary. In comparison, the annual influx of invertebrates carried upstream by incoming tides was estimated to be 1·9×10 6(6·2%; weighing 2·5 kg). Predominant in the downstream drift were the larvae/nymphs and/or pupae of chironomids, mayflies, stoneflies and caddisflies. The ' reverse ' drift comprised mainly copepods, ostracods, amphipods and oligochaetes. Mites and the brackishwater amphipod Gammarus zaddachicommonly moved in both directions. Highest drift densities occurred in July, whereas the lowest densities occurred in late autumn and winter. Multiple regression analysis showed no relationship between total drift or ' reverse ' drift densities and any of the measured environmental variables. Many of the freshwater invertebrates appeared not to die upon passing into tidal sections but resumed a benthic existence by virtue of varying degrees of salt tolerance. Of the three fish species common in the estuary, eel, common goby and flounder, the last two preyed measurably on freshwater taxa. Whereas gobies tended to be opportunistic feeders, depending on the section of estuary that they occupied, flounder were more restricted to the upper estuary where they fed selectively on chironomid larvae. On the latter diet, between March and September, the mean wet weight of flounders increased by more than 100 times (from 5 to 540 mg). Gobies were more numerous in the estuary from September to February, and although they ate insects their primary prey was G. zaddachi.

  17. Utilizing chromophoric dissolved organic matter measurements to derive export and reactivity of dissolved organic carbon exported to the Arctic Ocean: A case study of the Yukon River, Alaska

    USGS Publications Warehouse

    Spencer, R.G.M.; Aiken, G.R.; Butler, K.D.; Dornblaser, M.M.; Striegl, R.G.; Hernes, P.J.

    2009-01-01

    The quality and quantity of dissolved organic matter (DOM) exported by Arctic rivers is known to vary with hydrology and this exported material plays a fundamental role in the biogeochemical cycling of carbon at high latitudes. We highlight the potential of optical measurements to examine DOM quality across the hydrograph in Arctic rivers. Furthermore, we establish chromophoric DOM (CDOM) relationships to dissolved organic carbon (DOC) and lignin phenols in the Yukon River and model DOC and lignin loads from CDOM measurements, the former in excellent agreement with long-term DOC monitoring data. Intensive sampling across the historically under-sampled spring flush period highlights the importance of this time for total export of DOC and particularly lignin. Calculated riverine DOC loads to the Arctic Ocean show an increase from previous estimates, especially when new higher discharge data are incorporated. Increased DOC loads indicate decreased residence times for terrigenous DOM in the Arctic Ocean with important implications for the reactivity and export of this material to the Atlantic Ocean. Citation: Spencer, R. G. M., G. R. Aiken, K. D. Butler, M. M. Dornblaser, R. G. Striegl, and P. J. Hernes (2009), Utilizing chromophoric dissolved organic matter measurements to derive export and reactivity of dissolved organic carbon exported to the Arctic Ocean: A case study of the Yukon River, Alaska, Geophys. Res. Lett., 36, L06401, doi:10.1029/ 2008GL036831. Copyright 2009 by the American Geophysical Union.

  18. Carbon export efficiency and phytoplankton community composition in the Atlantic sector of the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Moigne, Frédéric A. C.; Poulton, Alex J.; Henson, Stephanie A.; Daniels, Chris J.; Fragoso, Glaucia M.; Mitchell, Elaine; Richier, Sophie; Russell, Benjamin C.; Smith, Helen E. K.; Tarling, Geraint A.; Young, Jeremy R.; Zubkov, Mike

    2015-06-01

    Arctic primary production is sensitive to reductions in sea ice cover, and will likely increase into the future. Whether this increased primary production (PP) will translate into increased export of particulate organic carbon (POC) is currently unclear. Here we report on the POC export efficiency during summer 2012 in the Atlantic sector of the Arctic Ocean. We coupled 234-thorium based estimates of the export flux of POC to onboard incubation-based estimates of PP. Export efficiency (defined as the fraction of PP that is exported below 100 m depth: ThE-ratio) showed large variability (0.09 ± 0.19-1.3 ± 0.3). The highest ThE-ratio (1.3 ± 0.3) was recorded in a mono-specific bloom of Phaeocystis pouchetii located in the ice edge. Blooming diatom dominated areas also had high ThE-ratios (0.1 ± 0.1-0.5 ± 0.2), while mixed and/or prebloom communities showed lower ThE-ratios (0.10 ± 0.03-0.19 ± 0.05). Furthermore, using oxygen saturation, bacterial abundance, bacterial production, and zooplankton oxygen demand, we also investigated spatial variability in the degree to which this sinking material may be remineralized in the upper mesopelagic (<300 m). Our results suggest that blooming diatoms and P. pouchetii can export a significant fraction of their biomass below the surface layer (100 m) in the open Arctic Ocean. Also, we show evidence that the material sinking from a P. pouchetii bloom may be remineralized (>100 m) at a similar rate as the material sinking from diatom blooms in the upper mesopelagic, contrary to previous findings.

  19. The uptake and export of silicon and nitrogen in HNLC waters of the NE Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Whitney, Frank A.; Crawford, David W.; Yoshimura, Takeshi

    2005-04-01

    The high-nitrate, low-chlorophyll (HNLC) waters of the Gulf of Alaska tend towards silicate rather than nitrate depletion as phytoplankton utilize nutrients during summer. This tendency is enhanced when iron supply is elevated through natural inputs such as from coastally generated mesoscale eddies or through artificial enrichment as was carried out in an in situ experiment in July 2002. However, ship-board incubations with iron enrichment demonstrate nitrate rather than silicate depletion for these waters. The difference between in situ and in vitro experiments occurs at least in part because deck incubations do not allow export of particulate Si and N. Due to the more efficient recycling of nitrogen and carbon, export favours the removal of silicon from the upper ocean (the Si pump). Previous measurements at Ocean Station Papa (50N, 145W) show that 25% of the Si, but only 7% of the C and 4% of the N utilized during spring growth, is exported to a depth of 200 m. These results in the Gulf of Alaska agree with the present understanding of phytoplankton controls in other HNLC regions and show that any estimates of carbon export from iron enrichment should be based on Si- rather than N-limitation.

  20. Correlations Between Sea-Surface Salinity Tendencies and Freshwater Fluxes in the Pacific Ocean

    NASA Technical Reports Server (NTRS)

    Li, Zhen; Adamec, David

    2007-01-01

    Temporal changes in sea-surface salinity (SSS) from 21 years of a high resolution model integration of the Pacific Ocean are correlated with the freshwater flux that was used to force the integration. The correlations are calculated on a 1 x10 grid, and on a monthly scale to assess the possibility of deducing evaporation minus precipitation (E-P) fields from the salinity measurements to be taken by the upcoming Aquarius/SAC-D mission. Correlations between the monthly mean E-P fields and monthly mean SSS temporal tendencies are mainly zonally-oriented, and are highest where the local precipitation is relatively high. Nonseasonal (deviations from the monthly mean) correlations are highest along mid-latitude storm tracks and are relatively small in the tropics. The response of the model's surface salinity to surface forcing is very complex, and retrievals of freshwater fluxes from SSS measurements alone will require consideration of other processes, including horizontal advection and vertical mixing, rather than a simple balance between the two.

  1. Oceanic Fluxes of Mass, Heat and Freshwater: A Global Estimate and Perspective

    NASA Technical Reports Server (NTRS)

    MacDonald, Alison Marguerite

    1995-01-01

    Data from fifteen globally distributed, modern, high resolution, hydrographic oceanic transects are combined in an inverse calculation using large scale box models. The models provide estimates of the global meridional heat and freshwater budgets and are used to examine the sensitivity of the global circulation, both inter and intra-basin exchange rates, to a variety of external constraints provided by estimates of Ekman, boundary current and throughflow transports. A solution is found which is consistent with both the model physics and the global data set, despite a twenty five year time span and a lack of seasonal consistency among the data. The overall pattern of the global circulation suggested by the models is similar to that proposed in previously published local studies and regional reviews. However, significant qualitative and quantitative differences exist. These differences are due both to the model definition and to the global nature of the data set.

  2. Upper ocean heat and freshwater budgets in the eastern Pacific warm pool

    NASA Astrophysics Data System (ADS)

    Wijesekera, Hemantha W.; Rudnick, Daniel L.; Paulson, Clayton A.; Pierce, Stephen D.; Pegau, W. Scott; Mickett, John; Gregg, Michael C.

    2005-08-01

    This study focuses on upper ocean budgets of heat and freshwater, which yield estimates of net surface heat flux and rainfall minus evaporation. The budgets are based on a 19 day ship survey conducted as part of the Eastern Pacific Investigation of Climate Processes in the Coupled Ocean-Atmosphere System 2001 in September 2001. Underway measurements included temperature and salinity sections from an undulating platform, SeaSoar, and horizontal currents from an acoustic Doppler current profiler along a 146 146 km survey pattern centered near 10N, 95W in the eastern Pacific warm pool. Additional measurements from a second ship at the center of the survey pattern included radar backscatter from rainfall, air-sea fluxes, and vertical profiles of temperature, salinity, microstructure, and horizontal velocity. Satellite measurements of surface height, temperature, and rainfall were also analyzed. The heat budget of 20 and 25 m surface layers indicated that storage, advection, turbulent transport, and penetrative solar radiation were all significant components of the heat budget with a net surface cooling of 41 W m-2 estimated as a residual, which agreed with atmospheric measurements (30 W m-2). The precipitation rate from the freshwater budget was 29 mm d-1, which was in excellent agreement with in situ measurements on both ships and in good agreement with satellite estimates for the same period. Lateral transports of heat and salt were influenced by an anticyclonic eddy in the survey area, and it is suggested that anticyclonic eddies, which form near the Central American coast, may carry anomalously warm sea surface temperature toward the west and become preferential sites for heavy rainfall.

  3. A linkage between Asian dust, dissolved iron and marine export production in the deep ocean

    NASA Astrophysics Data System (ADS)

    Han, Yongxiang; Zhao, Tianliang; Song, Lianchun; Fang, Xiaomin; Yin, Yan; Deng, Zuqin; Wang, Suping; Fan, Shuxian

    2011-08-01

    Iron-addition experiments have revealed that iron supply exerts controls on biogeochemical cycles in the ocean and ultimately influences the Earth's climate system. The iron hypothesis in its broad outlines has been proved to be correct. However, the hypothesis needs to be verified with an observable biological response to specific dust deposition events. Plankton growth following the Asian dust storm over Ocean Station PAPA (50N, 145W) in the North Pacific Ocean in April 2001 was the first supportive evidence of natural aeolian iron inputs to ocean; The data were obtained through the SeaWiFS satellite and robot carbon explorers by Bishop et al. Using the NARCM modeling results in this study, the calculated total dust deposition flux was 35 mg m -2 per day in PAPA region from the dust storm of 11-13 April, 2001 into 0.0615 mg m -2 d -1 (about 1100 nM) soluble iron in the surface layer at Station PAPA. It was enough for about 1100 nM to enhance the efficiency of the marine biological pump and trigger the rapid increase of POC and chlorophyll. The iron fertilization hypothesis therefore is plausible. However, even if this specific dust event can support the iron fertilization hypothesis, long-term observation data are lacking in marine export production and continental dust. In this paper, we also conducted a simple correlation analysis between the diatoms and foraminifera at about 3000 m and 4000 m at two subarctic Pacific stations and the dust aerosol production from China's mainland. The correlation coefficient between marine export production and dust storm frequency in the core area of the dust storms was significantly high, suggesting that aerosols generated by Asian dust storm are the source of iron for organic matter fixation in the North Pacific Ocean. These results suggest that there could be an interlocking chain for the change of atmospheric dust aerosol-soluble iron-marine export production.

  4. Does Saharan dust deposition influence the export of particle fluxes in the tropical North Atlantic Ocean?

    NASA Astrophysics Data System (ADS)

    Korte, Laura; van der Does, Michlle; Munday, Chris; Brummer, Geert-Jan; Stuut, Jan-Berend

    2015-04-01

    Every year over 200 million tons of Saharan dust are blown over the Atlantic Ocean towards the Caribbean. On its journey most of the dust is removed from the atmosphere by either dry or wet deposition and is ending up in the ocean. Its input potentially stimulates phytoplankton growth and possibly also drags down organic matter through the water column to the sea floor. The role of dust as a means to export organic carbon from the surface ocean to the deep is still controversially discussed. However, aggregation plays a critical role in carbon export since sinking velocities depend amongst others on particle constituents, size and shape, porosity and way of formation. Higher sinking velocities lead to less degradation and remineralization, or, in other words: fresher material. Here we present particle fluxes from one year (October 2012 until November 2013) collected by three sediment traps at 1200 m depth along a profile across the tropical North Atlantic Ocean. Average total mass fluxes vary between 40 and 111 mg/m2/d depending on the location in the ocean. Peak fluxes of 230 and 270 mg/m2/d in the second half of April and by the end of October/start of November 2013 in the western tropical ocean are worth mentioning since they differ in nature; carbonaceous material dominate fluxes in spring and biogenic opal in autumn. The calculated rest fractions, which we interpret as wind-blown dust, vary between 41 mg/m2/d closest to the African coast, and 10 to 18 mg/m2/d to the western open ocean. Total organic carbon (TOC) and biogenic opal are related to the rest fraction for two traps; this relation improves with distance to the source. Unexpectedly, the rest fraction of the sediment trap closest to the African coast, do neither show a relation to organic matter nor to biogenic opal. Same findings hold true for the ?15Ntot values of the material: they correlate negatively with the rest fraction, indicating fresher material. These correlations become stronger to the West Atlantic Ocean. Nevertheless, we speculate that Saharan dust deposition might influence the export and freshness of particles in the North Atlantic Ocean.

  5. Southern Ocean deep-water carbon export enhanced by natural iron fertilization.

    PubMed

    Pollard, Raymond T; Salter, Ian; Sanders, Richard J; Lucas, Mike I; Moore, C Mark; Mills, Rachel A; Statham, Peter J; Allen, John T; Baker, Alex R; Bakker, Dorothee C E; Charette, Matthew A; Fielding, Sophie; Fones, Gary R; French, Megan; Hickman, Anna E; Holland, Ross J; Hughes, J Alan; Jickells, Timothy D; Lampitt, Richard S; Morris, Paul J; Ndlec, Florence H; Nielsdttir, Maria; Planquette, Hlne; Popova, Ekaterina E; Poulton, Alex J; Read, Jane F; Seeyave, Sophie; Smith, Tania; Stinchcombe, Mark; Taylor, Sarah; Thomalla, Sandy; Venables, Hugh J; Williamson, Robert; Zubkov, Mike V

    2009-01-29

    The addition of iron to high-nutrient, low-chlorophyll regions induces phytoplankton blooms that take up carbon. Carbon export from the surface layer and, in particular, the ability of the ocean and sediments to sequester carbon for many years remains, however, poorly quantified. Here we report data from the CROZEX experiment in the Southern Ocean, which was conducted to test the hypothesis that the observed north-south gradient in phytoplankton concentrations in the vicinity of the Crozet Islands is induced by natural iron fertilization that results in enhanced organic carbon flux to the deep ocean. We report annual particulate carbon fluxes out of the surface layer, at three kilometres below the ocean surface and to the ocean floor. We find that carbon fluxes from a highly productive, naturally iron-fertilized region of the sub-Antarctic Southern Ocean are two to three times larger than the carbon fluxes from an adjacent high-nutrient, low-chlorophyll area not fertilized by iron. Our findings support the hypothesis that increased iron supply to the glacial sub-Antarctic may have directly enhanced carbon export to the deep ocean. The CROZEX sequestration efficiency (the amount of carbon sequestered below the depth of winter mixing for a given iron supply) of 8,600 mol mol(-1) was 18 times greater than that of a phytoplankton bloom induced artificially by adding iron, but 77 times smaller than that of another bloom initiated, like CROZEX, by a natural supply of iron. Large losses of purposefully added iron can explain the lower efficiency of the induced bloom(6). The discrepancy between the blooms naturally supplied with iron may result in part from an underestimate of horizontal iron supply. PMID:19177128

  6. Investigation on mechanisms controlling export production at the LGM with an biogeochemical ocean model

    NASA Astrophysics Data System (ADS)

    Oka, A.; Abe-Ouchi, A.; Chikamoto, M.; Ide, T.

    2012-04-01

    Using a biogeochemical ocean model that includes the iron cycle, we carry out preindustrial (control, CTL) and glacial (Last Glacial Maximum, LGM) climate simulations and investigate difference in export production (EP) between CTL and LGM. The model successfully reproduces general trends of a paleoclimate reconstruction of EP at the LGM except over the Atlantic Ocean. By conducting a series of sensitivity simulations, we investigate the mechanism controlling EP at the LGM in each basin. In the Southern Ocean, the model successfully reproduces the dipole pattern of the paleo reconstruction: the higher-latitude decrease and lower-latitude increase of EP. It is found that the lower-latitude increase of EP comes from iron fertilization effects by enhanced dust deposition, while the higher-latitude decrease of EP is caused by the reduction of surface shortwave due to spreading of sea ice there. We also find that increased dust input in other basins remotely affects EP in the Southern Ocean. In the Atlantic Ocean where the model fails to reproduce the paleo reconstruction, it is demonstrated that the response of EP in the Atlantic Ocean is strongly affected by distribution of iron limitation in a control climate. It is implied that the accurate evaluation of iron limitation in the present ocean is critical for evaluating changes in EP and associated reduction of atmospheric CO2 concentration at the LGM.

  7. Climate change increases riverine carbon outgassing while export to the ocean remains uncertain

    NASA Astrophysics Data System (ADS)

    Langerwisch, F.; Walz, A.; Rammig, A.; Tietjen, B.; Thonicke, K.; Cramer, W.

    2015-08-01

    Carbon fluxes in the Amazon Basin are considerably influenced by annual flooding during which terrigenous organic material is imported to the river. This regular interaction affects carbon pools within the riverine system, terrestrial carbon, and carbon exported to the ocean and released to the atmosphere. The processes of generation, conversion, and transport of organic carbon in this coupled terrigenous-riverine system strongly interact and are climate-sensitive, yet their response to climate change is still largely unknown. To quantify climate change effects on carbon pools and on carbon fluxes within the river and to the ocean and the atmosphere, we developed the riverine carbon model RivCM, which is directly coupled to the well-established dynamic vegetation and hydrology model LPJmL. We show here that RivCM successfully reproduces observed values in exported carbon and riverine carbon concentration. We evaluate future changes in riverine carbon by applying RivCM for climate forcing from five climate models and three CO2 emission scenarios (SRES). We find that climate change causes a doubling of riverine organic carbon in the Southern and Western basin while reducing it by 20 % in the eastern and northern parts. In contrast, the amount of riverine inorganic carbon shows a 2- to 3-fold increase in the entire basin, independent of the SRES scenario. The export of carbon to the atmosphere increases as well with an average of about 30 %. In contrast, changes in future export of organic carbon to the Atlantic Ocean depend on the SRES scenario and are projected to either decrease by about 8.9 % (SRES A1B) or increase by about 9.1 % (SRES A2). Such changes in the terrigenous-riverine system could have local and regional impacts on the carbon budget of the whole Amazon Basin and parts of the Atlantic Ocean. Changes in the riverine carbon could lead to a shift in the riverine nutrient supply and pH, while changes in the exported carbon to the ocean leads to changes in the supply of organic material that acts as food source in the Atlantic. On the larger scale the increased outgassing of CO2 could turn the Amazon Basin from a sink of carbon to a considerable source. Therefore we propose that the coupling of terrestrial and riverine carbon budget should be included in subsequent analysis of the future regional carbon budget.

  8. Interannual and Spatial Variability of Global Ocean Heat/Freshwater Content Identified from GTSPP

    NASA Astrophysics Data System (ADS)

    Chu, P. C.; Sun, C.

    2013-12-01

    Global Temperature and Salinity Profile Program (GTSPP) is a cooperative international project since 1990. The GTSPP handles all temperature and salinity profile data including XBT, CTDs, thermistor chain data, and Argo observations. Near-real time gridded (T, S) dataset was established from GTSPP since 1990 with horizontal resolution of (1o1o) and temporal increment of 1 month using the recently developed optimal spectral decomposition (OSD) method. With this new monthly varying gridded dataset, the upper ocean (surface to 300 m depth) heat content OHC300 and freshwater content FWC300 were calculated at each horizontal grid point. The empirical orthogonal function (EOF) analysis was conducted on the temporally varying global 2D OHC300 anomaly relative to its seasonal variation. A new phenomenon, global ocean tripole, was discovered. The EOF-1 mode (44.2% variance) represents the classical El Nino/La Nina phenomenon. The EOF-2 mode (14.6%) represents the Indian Ocean Dipole mode and the El Nino Modoki. Its features and connection to climate variability is also discussed. The empirical orthogonal function (EOF) analysis was conducted on the temporally varying global 2D FWC300 anomaly relative to its seasonal variation. The EOF-1 mode (73.7% variance) represents near global-scale variability with the largest anomaly appearing in the Indian Ocean near southeast of Africa. The first principal component (PC1) shows decadal variability. The temporal-spatial variability represented by the EOF-1 mode shows rapid increasing of global FWC300 from 1999 to 2005 and sustaining the high values after 2005. Interpretations of the observational results to recent global warming will also be presented.

  9. A probabilistic assessment of calcium carbonate export and dissolution in the modern ocean

    NASA Astrophysics Data System (ADS)

    Battaglia, G.; Steinacher, M.; Joos, F.

    2015-12-01

    The marine cycle of calcium carbonate (CaCO3) is an important element of the carbon cycle and co-governs the distribution of carbon and alkalinity within the ocean. However, CaCO3 fluxes and mechanisms governing CaCO3 dissolution are highly uncertain. We present an observationally-constrained, probabilistic assessment of the global and regional CaCO3 budgets. Parameters governing pelagic CaCO3 export fluxes and dissolution rates are sampled using a Latin-Hypercube scheme to construct a 1000 member ensemble with the Bern3D ocean model. Ensemble results are constrained by comparing simulated and observation-based fields of excess dissolved calcium carbonate (TA*). The minerals calcite and aragonite are modelled explicitly and ocean-sediment fluxes are considered. For local dissolution rates either a strong, a weak or no dependency on CaCO3 saturation is assumed. Median (68 % confidence interval) global CaCO3 export is 0.82 (0.67-0.98) Gt PIC yr-1, within the lower half of previously published estimates (0.4-1.8 Gt PIC yr-1). The spatial pattern of CaCO3 export is broadly consistent with earlier assessments. Export is large in the Southern Ocean, the tropical Indo-Pacific, the northern Pacific and relatively small in the Atlantic. Dissolution within the 200 to 1500 m depth range (0.33; 0.26-0.40 Gt PIC yr-1) is substantially lower than inferred from the TA*-CFC age method (1 ± 0.5 Gt PIC yr-1). The latter estimate is likely biased high as the TA*-CFC method neglects transport. The constrained results are robust across a range of diapycnal mixing coefficients and, thus, ocean circulation strengths. Modelled ocean circulation and transport time scales for the different setups were further evaluated with CFC11 and radiocarbon observations. Parameters and mechanisms governing dissolution are hardly constrained by either the TA* data or the current compilation of CaCO3 flux measurements such that model realisations with and without saturation-dependent dissolution achieve skill. We suggest to apply saturation-independent dissolution rates in Earth System Models to minimise computational costs.

  10. Silicate deposition during decomposition of cyanobacteria may promote export of picophytoplankton to the deep ocean.

    PubMed

    Tang, Tiantian; Kisslinger, Kim; Lee, Cindy

    2014-01-01

    Marine particles transport organic matter through the water column to the sediment where the organic matter can be buried. This pathway is one of the few natural removal mechanisms of CO2 from the atmosphere over geological time. Picophytoplankton, major primary producers in the ocean, have until recently been thought unimportant regarding particle transport. Here we provide evidence that silicate is deposited on extracellular polymeric substance (EPS) associated with decomposing picophytoplankton. We also find that Si is enriched in a previously unexplored group of marine particles (called micro-blebs) from the deep-water column. The surprising similarity in morphology and composition between EPS-Si and micro-blebs suggests that EPS-Si may be a precursor of micro-blebs observed in the deep ocean. This previously unexplored source of silicon may be important to silicon cycling and may further enhance export of picophytoplankton to the deep ocean. PMID:24920300

  11. Magnitude of the freshwater turtle exports from the US: long term trends and early effects of newly implemented harvest management regimes.

    PubMed

    Mali, Ivana; Vandewege, Michael W; Davis, Scott K; Forstner, Michael R J

    2014-01-01

    Unregulated commercial harvest remains a major threat for turtles across the globe. Due to continuing demand from Asian markets, a significant number of turtles are exported from the United States of America (US). Beginning in 2007, several southeastern states in the US implemented restrictions on the commercial harvest of turtles, in order to address the unsustainable take. We have summarized freshwater turtle exports from the US between 2002 and 2012 and demonstrated that the magnitude of turtle exports from the US remained high although the exports decreased throughout the decade. Louisiana and California were the major exporters. The majority of exports were captive bred, and from two genera, Pseudemys and Trachemys. We review the changes over the decade and speculate that the increase in export of wild turtles out of Louisiana after 2007 could be a consequence of strict regulations in surrounding states (e.g., Alabama, Florida). We suggest that if wild turtle protection is a goal for conservation efforts, then these states should work together to develop comprehensive regulation reforms pertaining to the harvest of wild turtles. PMID:24475128

  12. Magnitude of the Freshwater Turtle Exports from the US: Long Term Trends and Early Effects of Newly Implemented Harvest Management Regimes

    PubMed Central

    Mali, Ivana; Vandewege, Michael W.; Davis, Scott K.; Forstner, Michael R. J.

    2014-01-01

    Unregulated commercial harvest remains a major threat for turtles across the globe. Due to continuing demand from Asian markets, a significant number of turtles are exported from the United States of America (US). Beginning in 2007, several southeastern states in the US implemented restrictions on the commercial harvest of turtles, in order to address the unsustainable take. We have summarized freshwater turtle exports from the US between 2002 and 2012 and demonstrated that the magnitude of turtle exports from the US remained high although the exports decreased throughout the decade. Louisiana and California were the major exporters. The majority of exports were captive bred, and from two genera, Pseudemys and Trachemys. We review the changes over the decade and speculate that the increase in export of wild turtles out of Louisiana after 2007 could be a consequence of strict regulations in surrounding states (e.g., Alabama, Florida). We suggest that if wild turtle protection is a goal for conservation efforts, then these states should work together to develop comprehensive regulation reforms pertaining to the harvest of wild turtles. PMID:24475128

  13. Simulating the natural variability of the freshwater budget of the Arctic ocean from the mid to late Holocene using LOVECLIM

    NASA Astrophysics Data System (ADS)

    Davies, F. J.; Goosse, H.; Renssen, H.

    2012-04-01

    The influence of freshwater on the long term climatic variability of the Arctic region is currently of significant interest. Alterations to the natural variability of the oceanic, terrestrial and atmospheric sources of freshwater to the Arctic ocean, caused by anthropogenic induced warming, are likely to have far reaching effects on oceanic processes and climate. A number of these changes are already observable, such as an intensification of the hydrological cycle, a 7% increase in Eurasian river runoff (1936-1999), a 9% reduction of sea-ice extent per decade (1979-2006), a 120km northward migration of permafrost in Northern Canada (1968-1994), and air temperatures 6°C warmer, in parts, from 2007 to 2010, when compared to the 1958-1996 average. All of these changes add another layer of complexity to understanding the role of the freshwater budget, and this makes it difficult to say with any certainty how these future changes will impact freshwater fluxes of the Arctic gateways, such as the Bering Strait, Fram Strait, Canadian Arctic Archipelago and the Barents Sea inflow. Despite these difficulties, there have been studies that have integrated the available data, from both in situ measurements and modelling studies, and used this as a basis to form a picture of the current freshwater budget, and then project upon these hypotheses for the future (Holland et al., 2007). However, one particular aspect of these future projections that is lacking is the accountability of how much future variance is attributable to both natural variability and anthropogenic influences. Here we present results of a mid to late (6-0ka) Holocene transient simulation, using the earth model of intermediate complexity, LOVECLIM (Goosse et al., 2010). The model is forced with orbital and greenhouse gas forcings appropriate for the time period. The results will highlight the natural variability of the oceanic, terrestrial and atmospheric components of the freshwater budget, over decadal and centennial timescales. When computing the freshwater budget for the period, where in situ measurements are available, LOVECLIM has been shown to perform reasonably well. The intention here is not to present a fully quantitative assessment of the freshwater budget of the Arctic Ocean as such, but to highlight the natural variability of the freshwater budget and its individual components. We hope that this inspires other modelling groups to take a similar approach and work towards understanding the natural variability of the freshwater budget over timescales longer than current measurements allow, and modelling studies have previously attempted. Goosse, H., Brovkin, V., Fichefet, T., Haarsma, R., Huybrechts, P., Jongma, J., Mouchet, A., Selten, F., Barriat, P-Y., Campin, J-M., Deleersnijder, E., Driesschaert, E., Goelzer, H., Janssens, I., Loutre, M-F., Morales Maqueda, M.A., Opsteegh, T., Mathieu, P-P., Munhoven, G., Pettersson, E.J., Renssen, H., Roche, D.M., Schaeffer, M., Tartinville, B., Timmermann, A., Weber, S.L. (2010) Description of the Earth System Model of Intermediate Complexity LOVECLIM Version 1.2, Geoscientific Model Development, 3:603-633 doi: 10.5194/gmd-3-603-2010. Holland, M.M., Finnis, J., Barrett, A.P., Serreze, M.C. (2007) Projected Changes in Arctic Ocean Freshwater Budgets, Journal of Geophysical Research, 112, G04S55, doi:10.1029/2006JG000354, 2007

  14. Salinity changes in the World Ocean since 1950 in relation to changing surface freshwater fluxes

    NASA Astrophysics Data System (ADS)

    Skliris, Nikolaos; Marsh, Robert; Josey, Simon A.; Good, Simon A.; Liu, Chunlei; Allan, Richard P.

    2014-08-01

    Global hydrographic and air-sea freshwater flux datasets are used to investigate ocean salinity changes over 1950-2010 in relation to surface freshwater flux. On multi-decadal timescales, surface salinity increases (decreases) in evaporation (precipitation) dominated regions, the Atlantic-Pacific salinity contrast increases, and the upper thermocline salinity maximum increases while the salinity minimum of intermediate waters decreases. Potential trends in E-P are examined for 1950-2010 (using two reanalyses) and 1979-2010 (using four reanalyses and two blended products). Large differences in the 1950-2010 E-P trend patterns are evident in several regions, particularly the North Atlantic. For 1979-2010 some coherency in the spatial change patterns is evident but there is still a large spread in trend magnitude and sign between the six E-P products. However, a robust pattern of increased E-P in the southern hemisphere subtropical gyres is seen in all products. There is also some evidence in the tropical Pacific for a link between the spatial change patterns of salinity and E-P associated with ENSO. The water cycle amplification rate over specific regions is subsequently inferred from the observed 3-D salinity change field using a salt conservation equation in variable isopycnal volumes, implicitly accounting for the migration of isopycnal surfaces. Inferred global changes of E-P over 1950-2010 amount to an increase of 1 0.6 % in net evaporation across the subtropics and an increase of 4.2 2 % in net precipitation across subpolar latitudes. Amplification rates are approximately doubled over 1979-2010, consistent with accelerated broad-scale warming but also coincident with much improved salinity sampling over the latter period.

  15. Production of giant marine diatoms and their export at oceanic frontal zones: Implications for Si and C flux from stratified oceans

    NASA Astrophysics Data System (ADS)

    Kemp, A. E. S.; Pearce, R. B.; Grigorov, I.; Rance, J.; Lange, C. B.; Quilty, P.; Salter, I.

    2006-12-01

    From a synthesis of recent oceanic observations and paleo-data it is evident that certain species of giant diatoms including Rhizosolenia spp. Thalassiothrix spp. and Ethmodiscus rex may become concentrated at oceanic frontal zones and subsequently form episodes of mass flux to the sediment. Within the nutrient bearing waters advecting towards frontal boundaries, these species are generally not dominant, but they appear selectively segregated at fronts, and thus may dominate the export flux. Ancient Thalassiothrix diatom mat deposits in the eastern equatorial Pacific and beneath the Polar Front in the Southern Ocean record the highest open ocean sedimentation rates ever documented and represent vast sinks of silica and carbon. Several of the species involved are adapted to a stratified water column and may thrive in Deep Chlorophyll Maxima. Thus in oceanic regions and/or at times prone to enhanced surface water stratification (e.g., during meltwater pulses) they provide a mechanism for generating substantial biomass at depth and its subsequent export with concomitant implications for Si export and C drawdown. This ecology has important implications for ocean biogeochemical models suggesting that more than one diatom "functional type" should be used. In spite of the importance of these giant diatoms for biogeochemical cycling, their large size coupled with the constraints of conventional oceanographic survey schemes and techniques means that they are undersampled. An improved insight into these key species will be an important prerequisite for enhancing our understanding of marine biogeochemical cycling and for assessing the impacts of climate change on ocean export production.

  16. Satellite-based global-ocean mass balance estimates of interannual variability and emerging trends in continental freshwater discharge

    PubMed Central

    Syed, Tajdarul H.; Famiglietti, James S.; Chambers, Don P.; Willis, Josh K.; Hilburn, Kyle

    2010-01-01

    Freshwater discharge from the continents is a key component of Earth’s water cycle that sustains human life and ecosystem health. Surprisingly, owing to a number of socioeconomic and political obstacles, a comprehensive global river discharge observing system does not yet exist. Here we use 13 years (1994–2006) of satellite precipitation, evaporation, and sea level data in an ocean mass balance to estimate freshwater discharge into the global ocean. Results indicate that global freshwater discharge averaged 36,055 km3/y for the study period while exhibiting significant interannual variability driven primarily by El Niño Southern Oscillation cycles. The method described here can ultimately be used to estimate long-term global discharge trends as the records of sea level rise and ocean temperature lengthen. For the relatively short 13-year period studied here, global discharge increased by 540 km3/y2, which was largely attributed to an increase of global-ocean evaporation (768 km3/y2). Sustained growth of these flux rates into long-term trends would provide evidence for increasing intensity of the hydrologic cycle. PMID:20921364

  17. Satellite-based global-ocean mass balance estimates of interannual variability and emerging trends in continental freshwater discharge.

    PubMed

    Syed, Tajdarul H; Famiglietti, James S; Chambers, Don P; Willis, Josh K; Hilburn, Kyle

    2010-10-19

    Freshwater discharge from the continents is a key component of Earth's water cycle that sustains human life and ecosystem health. Surprisingly, owing to a number of socioeconomic and political obstacles, a comprehensive global river discharge observing system does not yet exist. Here we use 13 years (1994-2006) of satellite precipitation, evaporation, and sea level data in an ocean mass balance to estimate freshwater discharge into the global ocean. Results indicate that global freshwater discharge averaged 36,055 km(3)/y for the study period while exhibiting significant interannual variability driven primarily by El Nio Southern Oscillation cycles. The method described here can ultimately be used to estimate long-term global discharge trends as the records of sea level rise and ocean temperature lengthen. For the relatively short 13-year period studied here, global discharge increased by 540 km(3)/y(2), which was largely attributed to an increase of global-ocean evaporation (768 km(3)/y(2)). Sustained growth of these flux rates into long-term trends would provide evidence for increasing intensity of the hydrologic cycle. PMID:20921364

  18. Increased ocean carbon export in the Sargasso Sea is countered by its enhanced mesopelagic attenuation

    NASA Astrophysics Data System (ADS)

    Lomas, M. W.; Steinberg, D. K.; Dickey, T.; Carlson, C. A.; Nelson, N. B.; Condon, R. H.; Bates, N. R.

    2009-10-01

    Photosynthetic CO2 uptake by oceanic phytoplankton and subsequent export of particulate organic carbon (POC) to the ocean interior comprises a globally significant biological carbon pump, controlled in part by the composition of the planktonic community. The strength and efficiency of this pump depends upon the balance of particle production in the euphotic zone and remineralization of those particles in the mesopelagic (defined here as depths between 150 and 300 m), but how these processes respond to climate-driven changes in the physical environment is not completely understood. In the Sargasso Sea, from 1996-2007, we have observed a decade-long >50% increase in euphotic zone integrated autotrophic biomass (estimated from chlorophyll TChl-a from the surface ocean, prokaryotic phytoplankton, primary production and shallow (150 m) POC export coinciding with a shift in the mean phase of the winter North Atlantic Oscillation (NAO) from consistently positive to neutral but variable. During this same period mesopelagic POC flux attenuation has doubled such that carbon sequestration below 300 m, the maximum winter/spring ventilation depth, has not changed. The increased mesopelagic POC attenuation appears mediated by changes in plankton community composition and metabolic activity in both the euphotic and mesopelagic zones which are counter to extant hypotheses regarding inter-relationships between phytoplankton community composition, productivity and carbon export, and have significant impacts on how the Sargasso Sea ecosystem, at least, is modeled. Moreover, these time-series observations suggest that processes in the euphotic zone and mesopelagic are tightly coupled and should be considered together in future research.

  19. Controls on and variability in particle export and flux attenuation in the ocean's twilight zone (Invited)

    NASA Astrophysics Data System (ADS)

    Buesseler, K.; Boyd, P. W.

    2010-12-01

    Pelagic foodwebs drive a flux of >10 Gt C yr-1 that exits surface waters, mostly via sinking particles through the oceans biological pump. Most of this particle flux is remineralized in the poorly studied waters of the twilight zone, i.e. the layer underlying the euphotic zone and extending to 1000 m. Changes in the the magnitude of this pump and the length scales of remineralization will impact oceanic CO2 uptake. It has been difficult to compare the strength and efficiency of the biological pump in the twilight zone between oceanic provinces/regions due to: 1) variability in methods (traps, radionuclides, other budgets/models), 2) a lack of data (fluxes and supporting process information), especially covering seasonal/annual time-scales, and 3) the metrics used to parameterize export efficiency and flux attenuation. This was the motivation behind a reanalysis of selected twilight zone data that led to a new conceptual framework which can be used to compare the strength and efficiency of the biological pump between different regions and seasons (Buesseler and Boyd, L&O, v54(4), 2009, 1210-1232). This analysis confirms that we need to be more careful in our consideration of regional variability in euphotic zone depths when we compare biological pump efficiencies and the processes that control these differences. To this end, we compare the ratio of POC flux at the base of the euphotic zone (Ez) to net primary production, called the Ez-ratio, to distinguish it from depth normalized flux export ratios (e-ratios). In addition, conventional curve fitting of particle flux data vs. depth (i.e. Martin et al., 1987) can skew our interpretation of twilight zone processes, and thus attenuation below Ez is parameterized by the ratio of POC flux 100 m below Ez to the flux at Ez. This transfer efficiency, T100, varies from <20% to 100%. These new metrics are used to separate the ocean into regions and times of high and low surface export and subsurface attenuation. This presentation will review our knowledge of flux variabiltiy and attenuation in the twilight zone and expand the analyses presented in Buesseler and Boyd (2009) to other sites and using other flux methods. What is also important to consider, are the spatial scales of net primary production and export, which likely differ and hence introduce another level of uncertainty in our ability to understand oceanic CO2 uptake and C export. At present, we have a poorly constrained estimate of carbon sequestration via the biological pump, which, along with our limited understanding of the processes that control its magnitude, hinders our ability to predict the strength of oceanic uptake of CO2 and how this will be altered by a changing climate.

  20. Plutonium and americium export to the north-east Pacific Ocean by Columbia River runoff

    NASA Astrophysics Data System (ADS)

    Beasley, T. M.; Ball, L. A.; Blakesley, B. A.

    1981-12-01

    Between July 1978 and July 1979, monthly samples of water collected near the mouth of the Columbia River were analyzed for Pu and Am to budget the annual quantity of these radionuclides exported to the adjacent coastal zone. During this period, approximately 70mCi of 239, 240Pu and 17 mCi of 241Am were carried by the river to the ocean. From the depositional history of a fine-grained sediment core raised from within the Columbia River estuary, an estimated 4-8 Ci of 239, 240Pu and 1-2 Ci of 241Am have entered the north-east Pacific Ocean by river transport since the late 1950s. This input would have increased the transuranic inventories in adjacent coastal sediments by at most 25 times those expected as a result of direct atmospheric fallout.

  1. Influence that interannual variations in Siberian river discharge have on redistribution of freshwater fluxes in Arctic Ocean and North Atlantic

    NASA Astrophysics Data System (ADS)

    Kuzin, V. I.; Platov, G. A.; Golubeva, E. N.

    2010-12-01

    A numerical simulation with a coupled sea-ice model of the Arctic and North Atlantic oceans is used to study the influence that the interannual variations in the Siberian river discharge have on the distribution and propagation of freshwater in this region. In numerical experiments we compared simulations with the use of observational data on the discharge of the most significant Siberian rivers (Ob, Yenisei, and Lena) against the results of climatic seasonally average variations of their discharges. This comparison showed that the interannual variations may have significant consequences despite their smallness when compared with oceanic-scale water transport. These consequences include (1) the intensification of either cyclonic or anticyclonic components of motion of the subsurface Arctic Ocean waters and, as a result, the redistribution of freshwater fluxes from Arctic regions between the Fram Strait and the straits of the Canadian Archipelago. A change in the store of fresh Arctic Ocean waters due to interannual variations in the Ob, Yenisei, and Lena discharges is approximately 400 km3, whereas the volume of water redirected in this regard, which forms a link between some straits, reaches 15 thousand km3. On the other hand, (2) insignificant changes in the propagation direction of freshwaters are multiply enhanced in the process of their motion in the North Atlantic as part of the subpolar gyre because of their smaller or larger involvement in the processes of vertical mixing. As a result of this, anomalies of freshwater develop considerably far from the river mouths, like in the region of the Azores islands, and are 5-6 times larger than the maximum values of the accumulated variability volumes of the river discharge.

  2. Comparative analysis of Japanese three-spined stickleback clades reveals the Pacific Ocean lineage has adapted to freshwater environments while the Japan Sea has not.

    PubMed

    Ravinet, Mark; Takeuchi, Naoko; Kume, Manabu; Mori, Seiichi; Kitano, Jun

    2014-01-01

    Divergent selection and adaptive divergence can increase phenotypic diversification amongst populations and lineages. Yet adaptive divergence between different environments, habitats or niches does not occur in all lineages. For example, the colonization of freshwater environments by ancestral marine species has triggered adaptive radiation and phenotypic diversification in some taxa but not in others. Studying closely related lineages differing in their ability to diversify is an excellent means of understanding the factors promoting and constraining adaptive evolution. A well-known example of the evolution of increased phenotypic diversification following freshwater colonization is the three-spined stickleback. Two closely related stickleback lineages, the Pacific Ocean and the Japan Sea occur in Japan. However, Japanese freshwater stickleback populations are derived from the Pacific Ocean lineage only, suggesting the Japan Sea lineage is unable to colonize freshwater. Using stable isotope data and trophic morphology, we first show higher rates of phenotypic and ecological diversification between marine and freshwater populations within the Pacific Ocean lineage, confirming adaptive divergence has occurred between the two lineages and within the Pacific Ocean lineage but not in the Japan Sea lineage. We further identified consistent divergence in diet and foraging behaviour between marine forms from each lineage, confirming Pacific Ocean marine sticklebacks, from which all Japanese freshwater populations are derived, are better adapted to freshwater environments than Japan Sea sticklebacks. We suggest adaptive divergence between ancestral marine populations may have played a role in constraining phenotypic diversification and adaptive evolution in Japanese sticklebacks. PMID:25460163

  3. Comparative Analysis of Japanese Three-Spined Stickleback Clades Reveals the Pacific Ocean Lineage Has Adapted to Freshwater Environments while the Japan Sea Has Not

    PubMed Central

    Ravinet, Mark; Takeuchi, Naoko; Kume, Manabu; Mori, Seiichi; Kitano, Jun

    2014-01-01

    Divergent selection and adaptive divergence can increase phenotypic diversification amongst populations and lineages. Yet adaptive divergence between different environments, habitats or niches does not occur in all lineages. For example, the colonization of freshwater environments by ancestral marine species has triggered adaptive radiation and phenotypic diversification in some taxa but not in others. Studying closely related lineages differing in their ability to diversify is an excellent means of understanding the factors promoting and constraining adaptive evolution. A well-known example of the evolution of increased phenotypic diversification following freshwater colonization is the three-spined stickleback. Two closely related stickleback lineages, the Pacific Ocean and the Japan Sea occur in Japan. However, Japanese freshwater stickleback populations are derived from the Pacific Ocean lineage only, suggesting the Japan Sea lineage is unable to colonize freshwater. Using stable isotope data and trophic morphology, we first show higher rates of phenotypic and ecological diversification between marine and freshwater populations within the Pacific Ocean lineage, confirming adaptive divergence has occurred between the two lineages and within the Pacific Ocean lineage but not in the Japan Sea lineage. We further identified consistent divergence in diet and foraging behaviour between marine forms from each lineage, confirming Pacific Ocean marine sticklebacks, from which all Japanese freshwater populations are derived, are better adapted to freshwater environments than Japan Sea sticklebacks. We suggest adaptive divergence between ancestral marine populations may have played a role in constraining phenotypic diversification and adaptive evolution in Japanese sticklebacks. PMID:25460163

  4. Climate change decouples oceanic primary and export productivity and organic carbon burial

    PubMed Central

    Lopes, Cristina; Kucera, Michal; Mix, Alan C.

    2015-01-01

    Understanding responses of oceanic primary productivity, carbon export, and burial to climate change is essential for model-based projection of biological feedbacks in a high-CO2 world. Here we compare estimates of productivity based on the composition of fossil diatom floras with organic carbon burial off Oregon in the Northeast Pacific across a large climatic transition at the last glacial termination. Although estimated primary productivity was highest during the Last Glacial Maximum, carbon burial was lowest, reflecting reduced preservation linked to low sedimentation rates. A diatom size index further points to a glacial decrease (and deglacial increase) in the fraction of fixed carbon that was exported, inferred to reflect expansion, and contraction, of subpolar ecosystems that today favor smaller plankton. Thus, in contrast to models that link remineralization of carbon to temperature, in the Northeast Pacific, we find dominant ecosystem and sea floor control such that intervals of warming climate had more efficient carbon export and higher carbon burial despite falling primary productivity. PMID:25453073

  5. Export fluxes in a naturally iron-fertilized area of the Southern Ocean - Part 2: Importance of diatom resting spores and faecal pellets for export

    NASA Astrophysics Data System (ADS)

    Rembauville, M.; Blain, S.; Armand, L.; Quéguiner, B.; Salter, I.

    2015-06-01

    The biological composition of the material exported to a moored sediment trap located under the winter mixed layer of the naturally fertilized Kerguelen Plateau in the Southern Ocean was studied over an annual cycle. Despite iron availability in spring, the annual particulate organic carbon (POC) export (98.2 mmol m-2) at 289 m was low, but annual biogenic silica export was significant (114 mmol m-2). This feature was related to the abundance of empty diatom cells and the ratio of full to empty cells exerted a first-order control in BSi : POC export stoichiometry of the biological pump. Chaetoceros Hyalochaete spp. and Thalassiosira antarctica resting spores were responsible for more than 60% of the annual POC flux that occurred during two very short export events of < 14 days in spring-summer. Relatively low diatom fluxes were observed over the remainder of the year. Faecal pellet contribution to annual carbon flux was lower (34%) and reached its seasonal maximum in autumn and winter (> 80%). The seasonal progression of faecal pellet types revealed a clear transition from small spherical shapes (small copepods) in spring, to larger cylindrical and ellipsoid shapes in summer (euphausiids and large copepods) and finally to large tabular shapes (salps) in autumn and winter. We propose in this high-biomass, low-export (HBLE) environment that small but highly silicified and fast-sinking resting spores are able to bypass the intense grazing pressure and efficient carbon transfer to higher trophic levels that are responsible for the low fluxes observed the during the remainder of the year. More generally our study also provides a statistical framework linking the ecological succession of diatom and zooplankton communities to the seasonality of carbon and silicon export within an iron-fertilized bloom region in the Southern Ocean.

  6. Origin of freshwater and polynya water in the Arctic Ocean halocline in summer 2007

    NASA Astrophysics Data System (ADS)

    Bauch, Dorothea; van der Loeff, Michiel Rutgers; Andersen, Nils; Torres-Valdes, Sinhue; Bakker, Karel; Abrahamsen, E. Povl

    2011-12-01

    Extremely low summer sea-ice coverage in the Arctic Ocean in 2007 allowed extensive sampling and a wide quasi-synoptic hydrographic and ?18O dataset could be collected in the Eurasian Basin and the Makarov Basin up to the Alpha Ridge and the East Siberian continental margin. With the aim of determining the origin of freshwater in the halocline, fractions of river water and sea-ice meltwater in the upper 150 m were quantified by a combination of salinity and ?18O in the Eurasian Basin. Two methods, applying the preformed phosphate concentration (PO *) and the nitrate-to-phosphate ratio (N/P), were compared to further differentiate the marine fraction into Atlantic and Pacific-derived contributions. While PO *-based assessments systematically underestimate the contribution of Pacific-derived waters, N/P-based calculations overestimate Pacific-derived waters within the Transpolar Drift due to denitrification in bottom sediments at the Laptev Sea continental margin. Within the Eurasian Basin a west to east oriented front between net melting and production of sea-ice is observed. Outside the Atlantic regime dominated by net sea-ice melting, a pronounced layer influenced by brines released during sea-ice formation is present at about 30-50 m water depth with a maximum over the Lomonosov Ridge. The geographically distinct definition of this maximum demonstrates the rapid release and transport of signals from the shelf regions in discrete pulses within the Transpolar Drift. The ratio of sea-ice derived brine influence and river water is roughly constant within each layer of the Arctic Ocean halocline. The correlation between brine influence and river water reveals two clusters that can be assigned to the two main mechanisms of sea-ice formation within the Arctic Ocean. Over the open ocean or in polynyas at the continental slope where relatively small amounts of river water are found, sea-ice formation results in a linear correlation between brine influence and river water at salinities of about 32-34. In coastal polynyas in the shallow regions of the Laptev Sea and southern Kara Sea, sea-ice formation transports river water into the shelfs bottom layer due to the close proximity to the river mouths. This process therefore results in waters that form a second linear correlation between brine influence and river water at salinities of about 30-32. Our study indicates which layers of the Arctic Ocean halocline are primarily influenced by sea-ice formation in coastal polynyas and which layers are primarily influenced by sea-ice formation over the open ocean. Accordingly we use the ratio of sea-ice derived brine influence and river water to link the maximum in brine influence within the Transpolar Drift with a pulse of shelf waters from the Laptev Sea that was likely released in summer 2005.

  7. Signature of organic matter exported from naturally Fe-fertilised oceanic waters

    NASA Astrophysics Data System (ADS)

    Hernandez-Sanchez, Maria T.; Holtvoeth, Jens; Mills, Rachel A.; Fisher, Elizabeth H.; Wolff, George A.; Pancost, Richard D.

    Biomarker distributions and organic carbon and nitrogen isotopic signatures of organic matter (OM) produced in surface waters around the Crozet Plateau (Southern Ocean) are significantly different between a Fe-fertilised region (north) and a high nutrient low chlorophyll region (HNLC, south). If these OM signatures are exported to and preserved in surface sediments, they could potentially be used as palaeo-proxies for identifying Fe-fertilisation events in the past. Here, we assess the alteration of the OM signature through the water column and at the sediment-water interface by comparing organic signatures in surface waters, sediment traps and surface sediments. Our results suggest that there is significant degradation of OM during transport to the sea floor, which causes reduced fluxes of biomarkers to sediments north and east of the Crozet Plateau. Sterols, alkenones and C27 and C29 12-hydroxymethyl alkanoates, and C28 1,14-diols appear to be less labile than total organic carbon (TOC), except to the north, where alkenones and sterols are more rapidly degraded than TOC. Sedimentary bulk and compound specific ?13C values also reflect surface water productivity patterns, with elevated values occurring in sediments underlying the Fe-fertilised waters. In contrast, ?15N values appear to be strongly biased by degradation and grazing during export and burial. Thus, only some of the differences observed in surface waters between the Fe- fertilised and HNLC areas are exported to deep waters and preserved in the sedimentary record, suggesting that caution is required in the application of these proxies to studies of ocean palaeoproductivity.

  8. A Giant Arctic Freshwater Pond at the end of the Early Eocene; Implications for Ocean Heat Transport and Carbon Cycling

    NASA Astrophysics Data System (ADS)

    Brinkhuis, H.; Schouten, S.; Collinson, M. E.; Sluijs, A.; Sinninghe-Damste, J. S.; Dickens, G. R.; Huber, M.; Cronin, T. M.; Bujak, J. P.; Stein, R.; Eldrett, J. S.; Harding, I. C.; Sangiorgi, F.

    2005-12-01

    In the last decades remains of the free-floating, fresh water fern Azolla have been found in unusually high abundances in basal middle Eocene (~48.5 Ma) marine sediments deposited in all Nordic seas. While generally taken to signal some `freshwater input', their source and significance were not determined. Through palynological and organic geochemical analyses of unique cores obtained from unprecedented Arctic Ocean drilling (IODP 302 - ACEX) we show that the brackish surface conditions that prevailed in the Arctic Ocean through the late Paleocene and early Eocene culminated in the deposition of laminated organic rich deposits yielding huge amounts of remains of Azolla. This, plus e.g., low diversity dinoflagellate assemblages, and concomitant low BIT values, indicates in-situ Azolla growth, and that the surface of the Arctic Ocean episodically resembled a giant fresh water pond over an interval altogether lasting ~800,000 years. The Arctic Basin thus constituted the main source of the freshwater pulses found elsewhere, reaching as far south as the southern North Sea.TEX86-derived surface temperatures were 13-14C before and after the Azolla interval and only 10C during the event, which may be related to obstruction of pole ward ocean heat transport and/or increased carbon burial.

  9. Enhanced Particulate Organic Carbon Export at Eddy Edges in the Oligotrophic Western North Pacific Ocean

    PubMed Central

    Shih, Yung-Yen; Hung, Chin-Chang; Gong, Gwo-Ching; Chung, Wan-Chen; Wang, Yu-Huai; Lee, I-Huan; Chen, Kuo-Shu; Ho, Chuang-Yi

    2015-01-01

    Mesoscale eddies in the subtropical oligotrophic ocean are ubiquitous and play an important role in nutrient supply and oceanic primary production. However, it is still unclear whether these mesoscale eddies can efficiently transfer CO2 from the atmosphere to deep waters via biological pump because of the sampling difficulty due to their transient nature. In 2007, particulate organic carbon (POC) fluxes, measured below the euphotic zone at the edge of warm eddy were 136–194 mg-C m−2 d−1 which was greatly elevated over that (POC flux = 26–35 mg-C m−2 d−1) determined in the nutrient-depleted oligotrophic waters in the Western North Pacific (WNP). In 2010, higher POC fluxes (83–115 mg-C m−2 d−1) were also observed at the boundary of mesoscale eddies in the WNP. The enhanced POC flux at the edge of eddies was mainly attributed to both large denuded diatom frustules and zooplankton fecal pellets based on scanning electron microscopy (SEM) examination. The result suggests that mesoscale eddies in the oligotrophic waters in the subtropical WNP can efficiently increase the oceanic carbon export flux and the eddy edge is a crucial conduit in carbon sequestration to deep waters. PMID:26171611

  10. ENSO Modulations due to Interannual Variability of Freshwater Forcing and Ocean Biology-induced Heating in the Tropical Pacific

    PubMed Central

    Zhang, Rong-Hua; Gao, Chuan; Kang, Xianbiao; Zhi, Hai; Wang, Zhanggui; Feng, Licheng

    2015-01-01

    Recent studies have identified clear climate feedbacks associated with interannual variations in freshwater forcing (FWF) and ocean biology-induced heating (OBH) in the tropical Pacific. The interrelationships among the related anomaly fields are analyzed using hybrid coupled model (HCM) simulations to illustrate their combined roles in modulating the El Niño-Southern Oscillation (ENSO). The HCM-based supporting experiments are performed to isolate the related feedbacks, with interannually varying FWF and OBH being represented individually or collectively, which allows their effects to be examined in a clear way. It is demonstrated that the interannual freshwater forcing enhances ENSO variability and slightly prolongs the simulated ENSO period, while the interannual OBH reduces ENSO variability and slightly shortens the ENSO period, with their feedback effects tending to counteract each other. PMID:26678931

  11. ENSO Modulations due to Interannual Variability of Freshwater Forcing and Ocean Biology-induced Heating in the Tropical Pacific.

    PubMed

    Zhang, Rong-Hua; Gao, Chuan; Kang, Xianbiao; Zhi, Hai; Wang, Zhanggui; Feng, Licheng

    2015-01-01

    Recent studies have identified clear climate feedbacks associated with interannual variations in freshwater forcing (FWF) and ocean biology-induced heating (OBH) in the tropical Pacific. The interrelationships among the related anomaly fields are analyzed using hybrid coupled model (HCM) simulations to illustrate their combined roles in modulating the El Niño-Southern Oscillation (ENSO). The HCM-based supporting experiments are performed to isolate the related feedbacks, with interannually varying FWF and OBH being represented individually or collectively, which allows their effects to be examined in a clear way. It is demonstrated that the interannual freshwater forcing enhances ENSO variability and slightly prolongs the simulated ENSO period, while the interannual OBH reduces ENSO variability and slightly shortens the ENSO period, with their feedback effects tending to counteract each other. PMID:26678931

  12. ENSO Modulations due to Interannual Variability of Freshwater Forcing and Ocean Biology-induced Heating in the Tropical Pacific

    NASA Astrophysics Data System (ADS)

    Zhang, Rong-Hua; Gao, Chuan; Kang, Xianbiao; Zhi, Hai; Wang, Zhanggui; Feng, Licheng

    2015-12-01

    Recent studies have identified clear climate feedbacks associated with interannual variations in freshwater forcing (FWF) and ocean biology-induced heating (OBH) in the tropical Pacific. The interrelationships among the related anomaly fields are analyzed using hybrid coupled model (HCM) simulations to illustrate their combined roles in modulating the El Nio-Southern Oscillation (ENSO). The HCM-based supporting experiments are performed to isolate the related feedbacks, with interannually varying FWF and OBH being represented individually or collectively, which allows their effects to be examined in a clear way. It is demonstrated that the interannual freshwater forcing enhances ENSO variability and slightly prolongs the simulated ENSO period, while the interannual OBH reduces ENSO variability and slightly shortens the ENSO period, with their feedback effects tending to counteract each other.

  13. Chloropigment nitrogen isotopes: new insights on export production during oceanic anoxic events

    NASA Astrophysics Data System (ADS)

    Higgins, M. B.; Robinson, R. S.; Pearson, A.

    2011-12-01

    The Mesozoic is marked by several widespread occurrences of intense organic matter burial, corresponding to proposed Oceanic Anoxic Events (OAEs). Sediments from the largest of these events, the Cenomanian-Turonian OAE 2, are characterized by lower nitrogen isotope ratios than are seen in modern marine settings. We use a high-resolution porphyrin nitrogen isotope record through OAE 2 to interpret nitrogen isotope depletion that is common during OAEs. Nitrogen isotope values of sedimentary chloropigments reflect a diagenetically unaltered signal of surface water nitrogen sources. Additionally, due to taxonomic differences in chlorophyll nitrogen fractionation, the nitrogen isotopic offset between chloropigments and bulk nitrogen can be used to estimate the relative contribution of cyanobacteria and eukaryotic algae to export production. Our porphyrin data show that eukaryotes contributed the quantitative majority of export production throughout OAE 2, suggesting that any explanation for the OAE nitrogen cycle and its isotopic values be consistent with a eukaryote-dominated ecosystem. We propose that new production during OAE 2 primarily was driven by direct assimilation of upwelled NH4+, supplemented by diazotrophy. A marine nitrogen reservoir dominated by NH4+, in combination with known kinetic isotope effects, could lead to eukaryotic biomass depleted in 15N.

  14. New Biomarker Approaches for Investigating Export Productivity in the Post-K/Pg Living Ocean

    NASA Astrophysics Data System (ADS)

    Pancost, R.; Taylor, K. W.; Hollis, C. J.

    2012-12-01

    The long-term consequences of the Cretaceous-Paleogene (K/Pg) boundary event on the Earth system have been the subject of much scrutiny. Postulated climate events include a brief period of global cooling induced by sulphate aerosols (the so-called 'impact winter') and an interval of gradual warming caused by impact-induced CO2 release, as well as longer-term climatic oscillations during the subsequent 1 to 3Myr, including periods of sustained cooling. Associated with these were putative changes in the biogeochemical cycle, including suggestions that export production was much reduced and brought about a decrease in the deep to shallow water carbon isotope gradient. In this study we develop new biomarker-based climate and biogeochemical records for the mid-Waipara River section, NZ. We have used these to confirm hypotheses that: a) the post-K/Pg interval was characterised by a negative carbon isotope excursion, documented by both algal and higher plant biomarkers; b) that dramatic fluctuations in ocean temperature followed the K/Pg in the SW Pacific but that there was an overall cooling compared to the Late Cretaceous; c) that the terrestrial biosphere was affected bringing about decreased higher plant inputs to marginal marine sediments; and d) that the biological pump was less efficient during the first ca. 1 to 3 Myr of the Danian. Here we focus on the final aspect, proposing that the distribution of glycerol dialkyl glycerol tetraethers (GDGT) can be used not only as an ocean temperature proxy but to evaluate export production dynamics. We have shown that the ratio of GDGT-2/GDGT-3 (where numerals denote number of cyclopentyl moieties) increases with water column depth in modern and ancient oceans. In Waipara sediments spanning nearly 25 million years, 2/3 ratios are uniformly low (2-3); the only exception is the interval following the K/Pg boundary, during which they markedly increase to values of 6 to 10. We argue that this is evidence for a less efficient biological pump, i.e. the putative bias of GDGT export towards shallow waters was absent such that deeper waters represented a more prominent contribution to underlying sediments. This interpretation is consistent with a decrease in TOC contents and algal biomarker d13C values. We note, however, that there is little evidence for an algal extinction as a range of C27 to C30 sterols continued to be deposited throughout the entire section. Hence, we favour the 'Living Ocean' model for the SW Pacific during the interval following the K/Pg (as opposed to the more extreme 'Strangelove Ocean'), in which the biological pump was less effective but primary productivity was sustained.

  15. Export production and its regulating factors in the West Antarctica Peninsula region of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Huang, Kuan; Ducklow, Hugh; Vernet, Maria; Cassar, Nicolas; Bender, Michael L.

    2012-06-01

    In connection with the Palmer LTER program, mixed layer water samples were collected during the cruise of the L.M. Gould in Jan., 2008 at 49 stations on a 20 × 100 km grid in the West Antarctica Peninsula (WAP) region of the Southern Ocean. In this study, [O2]/[Ar] ratios and the triple isotope composition of dissolved O2 were measured, and were used to estimate net community O2 production (NCP) and gross primary O2production (GPP), respectively. These estimates are further converted to carbon export production, primary production and the f-ratio. Our measurements give NCP ranging from -3 to 76 mmol O2 m-2 day-1 (-25 to 650 mg C m-2 day-1), and GPP from 40 to 220 mmol O2 m-2 day-1 (180 to 1010 mg C m-2 day-1). The O2 NCP/GPP ratios range from -0.04 to 0.43, corresponding to f-ratios of -0.08 to 0.83. NCP and the NCP/GPP ratio are highest in the northern coastal areas, and decrease to lower values toward the southern coastal area and the open ocean. The inshore-offshore gradient appears to be regulated primarily by iron availability, as supported by the positive correlation between NCP and Fv/Fm ratios (r2 = 0.22, p < 0.05). Mixed layer depth (MLD) is inversely correlated with NCP (r2 = 0.21, p < 0.002) and NCP/GPP (r2 = 0.21, p < 0.02), and highest NCP occurred in the fresh water lenses probably formed from melted coastal glaciers. These results suggest that export production and the f-ratio increase where water stratification is intensified by input of fresh meltwater, and that mixed layer stratification is the major factor regulating NCP in the inner-shelf and coastal regions. Along-shelf variability of phytoplankton community composition is highly correlated with NCP, i.e., NCP increases when the diatom-dominated community in the south transitions to the cryptophyte-dominated one in the north. A high correlation is also observed between NCP and the logarithm of the surface chlorophyll concentration (r2 = 0.72, p < 0.0001) , which makes it possible to estimate carbon export as a function of Chl a concentration in this region.

  16. Persistent export of 231Pa from the deep central Arctic Ocean over the past 35,000 years.

    PubMed

    Hoffmann, Sharon S; McManus, Jerry F; Curry, William B; Brown-Leger, L Susan

    2013-05-30

    The Arctic Ocean has an important role in Earth's climate, both through surface processes such as sea-ice formation and transport, and through the production and export of waters at depth that contribute to the global thermohaline circulation. Deciphering the deep Arctic Ocean's palaeo-oceanographic history is a crucial part of understanding its role in climatic change. Here we show that sedimentary ratios of the radionuclides thorium-230 ((230)Th) and protactinium-231 ((231)Pa), which are produced in sea water and removed by particle scavenging on timescales of decades to centuries, respectively, record consistent evidence for the export of (231)Pa from the deep Arctic and may indicate continuous deep-water exchange between the Arctic and Atlantic oceans throughout the past 35,000 years. Seven well-dated box-core records provide a comprehensive overview of (231)Pa and (230)Th burial in Arctic sediments during glacial, deglacial and interglacial conditions. Sedimentary (231)Pa/(230)Th ratios decrease nearly linearly with increasing water depth above the core sites, indicating efficient particle scavenging in the upper water column and greater influence of removal by lateral transport at depth. Although the measured (230)Th burial is in balance with its production in Arctic sea water, integrated depth profiles for all time intervals reveal a deficit in (231)Pa burial that can be balanced only by lateral export in the water column. Because no enhanced sink for (231)Pa has yet been found in the Arctic, our records suggest that deep-water exchange through the Fram strait may export (231)Pa. Such export may have continued for the past 35,000 years, suggesting a century-scale replacement time for deep waters in the Arctic Ocean since the most recent glaciation and a persistent contribution of Arctic waters to the global ocean circulation. PMID:23719461

  17. Defluviimonas aquaemixtae sp. nov., isolated from the junction between a freshwater spring and the ocean.

    PubMed

    Jung, Yong-Taek; Park, Sooyeon; Lee, Jung-Sook; Yoon, Jung-Hoon

    2014-12-01

    A Gram-stain-negative, coccoid- or short-rod-shaped and non-gliding bacterial strain, designated CDM-7(T), was isolated from the zone where the ocean meets a freshwater spring at Jeju island, South Korea, and was subjected to a polyphasic taxonomic study. Strain CDM-7(T) grew optimally at pH 7.0-8.0, at 30 C and in the presence of 2-3?% (w/v) NaCl. Neighbour-joining, maximum-likelihood and maximum-parsimony phylogenetic trees based on 16S rRNA gene sequences showed that strain CDM-7(T) falls within the clade comprising species of the genus Defluviimonas, clustering with the type strain of Defluviimonas aestuarii, with which it exhibited the highest 16S rRNA gene sequence similarity value (98.4?%). The 16S rRNA gene sequence similarity values between strain CDM-7(T) and the type strains of Defluviimonas denitrificans and Defluviimonas indica were 97.1 and 96.2?%, respectively. The genomic DNA G+C content was 66.8 mol% and the mean DNA-DNA relatedness values between strain CDM-7(T) and the type strains of D. aestuarii and D. denitrificans were 15.62.5 and 6.73.2?%, respectively. Strain CDM-7(T) contained Q-10 as the predominant ubiquinone and summed feature 8 (C18?:?1?7c and/or C18?:?1?6c) as the major fatty acid. The major polar lipids were phosphatidylcholine, phosphatidylglycerol, an unidentified aminolipid, an unidentified phospholipid and an unidentified lipid. Differential phenotypic properties, together with the phylogenetic and genetic distinctiveness, demonstrated that strain CDM-7(T) is distinguishable from other species of the genus Defluviimonas. On the basis of the data presented, strain CDM-7(T) is considered to represent a novel species of the genus Defluviimonas, for which the name Defluviimonas aquaemixtae sp. nov. is proposed. The type strain is CDM-7(T) (?=?KCTC 42108(T)?=?CECT 8626(T)). PMID:25253071

  18. Glacial-Interglacial Changes in Export Production in the Subarctic North Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Kohfeld, K. E.; Chase, Z.

    2008-12-01

    The subarctic North Pacific Ocean is a key region for studying the linkages between circulation, dust, marine productivity, and carbon cycling, because it encompasses a high-nutrient low-chlorophyll region where iron addition experiments and direct observation of dust events have demonstrated its potential to drawdown atmospheric CO2. Furthermore, the deep North Pacific holds a large CO2 reservoir that is currently isolated from the atmosphere by a low-salinity layer, and it has recently been hypothesized that the re-organization of these high-CO2 waters may have played a crucial role in the degassing of carbon dioxide to the atmosphere during the last deglaciation. It is highly likely that this reorganization would leave some imprint on paleo-productivity records. Several studies of deep-sea cores from the North Pacific ocean have demonstrated that export production was greatly reduced during glacial periods. We used 230Th- normalization to reconstruct particle flux to an intermediate depth sediment core. RC10-196 (54.7N, 177.1E, 1007 m). This core has sedimentation rates ranging from 3-6 cm/1000 yr during the last 30,000 years. Lithogenic fluxes peak during the height of the last glacial period, while opal and carbonate fluxes peak abruptly on the deglaciation (at approximately 15,000 years ago). The timing of these increases in biogenic fluxes are consistent with those observed in deeper North Pacific cores, and are coincident with abrupt increases in North Pacific temperatures observed at 15,000 years ago. This correlation with temperature and the lack of correspondence between biogenic and lithogenic fluxes suggest that physical conditions may override the role of dust inputs in controlling productivity changes during the last glacial- interglacial transition. These data will be placed in the context of other records generated for the North Pacific Ocean, as part of a regional biogenic flux data synthesis.

  19. Impact of circulation on export production, dissolved organic matter, and dissolved oxygen in the ocean: Results from Phase II of the Ocean Carbon-cycle Model Intercomparison Project (OCMIP-2)

    NASA Astrophysics Data System (ADS)

    Najjar, R. G.; Jin, X.; Louanchi, F.; Aumont, O.; Caldeira, K.; Doney, S. C.; Dutay, J.-C.; Follows, M.; Gruber, N.; Joos, F.; Lindsay, K.; Maier-Reimer, E.; Matear, R. J.; Matsumoto, K.; Monfray, P.; Mouchet, A.; Orr, J. C.; Plattner, G.-K.; Sarmiento, J. L.; Schlitzer, R.; Slater, R. D.; Weirig, M.-F.; Yamanaka, Y.; Yool, A.

    2007-09-01

    Results are presented of export production, dissolved organic matter (DOM) and dissolved oxygen simulated by 12 global ocean models participating in the second phase of the Ocean Carbon-cycle Model Intercomparison Project. A common, simple biogeochemical model is utilized in different coarse-resolution ocean circulation models. The model mean (1?) downward flux of organic matter across 75 m depth is 17 6 Pg C yr-1. Model means of globally averaged particle export, the fraction of total export in dissolved form, surface semilabile dissolved organic carbon (DOC), and seasonal net outgassing (SNO) of oxygen are in good agreement with observation-based estimates, but particle export and surface DOC are too high in the tropics. There is a high sensitivity of the results to circulation, as evidenced by (1) the correlation of surface DOC and export with circulation metrics, including chlorofluorocarbon inventory and deep-ocean radiocarbon, (2) very large intermodel differences in Southern Ocean export, and (3) greater export production, fraction of export as DOM, and SNO in models with explicit mixed layer physics. However, deep-ocean oxygen, which varies widely among the models, is poorly correlated with other model indices. Cross-model means of several biogeochemical metrics show better agreement with observation-based estimates when restricted to those models that best simulate deep-ocean radiocarbon. Overall, the results emphasize the importance of physical processes in marine biogeochemical modeling and suggest that the development of circulation models can be accelerated by evaluating them with marine biogeochemical metrics.

  20. Arctic-HYCOS: a Large Sample observing system for estimating freshwater fluxes in the drainage basin of the Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Pietroniro, Al; Korhonen, Johanna; Looser, Ulrich; Hardardóttir, Jórunn; Johnsrud, Morten; Vuglinsky, Valery; Gustafsson, David; Lins, Harry F.; Conaway, Jeffrey S.; Lammers, Richard; Stewart, Bruce; Abrate, Tommaso; Pilon, Paul; Sighomnou, Daniel; Arheimer, Berit

    2015-04-01

    The Arctic region is an important regulating component of the global climate system, and is also experiencing a considerable change during recent decades. More than 10% of world's river-runoff flows to the Arctic Ocean and there is evidence of changes in its fresh-water balance. However, about 30% of the Arctic basin is still ungauged, with differing monitoring practices and data availability from the countries in the region. A consistent system for monitoring and sharing of hydrological information throughout the Arctic region is thus of highest interest for further studies and monitoring of the freshwater flux to the Arctic Ocean. The purpose of the Arctic-HYCOS project is to allow for collection and sharing of hydrological data. Preliminary 616 stations were identified with long-term daily discharge data available, and around 250 of these already provide online available data in near real time. This large sample will be used in the following scientific analysis: 1) to evaluate freshwater flux to the Arctic Ocean and Seas, 2) to monitor changes and enhance understanding of the hydrological regime and 3) to estimate flows in ungauged regions and develop models for enhanced hydrological prediction in the Arctic region. The project is intended as a component of the WMO (World Meteorological Organization) WHYCOS (World Hydrological Cycle Observing System) initiative, covering the area of the expansive transnational Arctic basin with participation from Canada, Denmark, Finland, Iceland, Norway, Russian Federation, Sweden and United States of America. The overall objective is to regularly collect, manage and share high quality data from a defined basic network of hydrological stations in the Arctic basin. The project focus on collecting data on discharge and possibly sediment transport and temperature. Data should be provisional in near-real time if available, whereas time-series of historical data should be provided once quality assurance has been completed. The initial stages of the project will focus on collecting data on discharge and revise station selection criteria. For monitoring freshwater flow to oceans, stations close to the mouths of rivers and immediately inland for back-up purposes will be preferred. For studies of change emphasis is placed on hydrological regime stations located in headwaters small sub-catchments, including pristine basins. Stations outside the Arctic Ocean basin, such as at the mouth of the Yukon River, Baltic Sea and Hudson Bay, can also be considered to allow a better understanding of hydrological processes occurring in the general region. Countries shall facilitate, to the extent possible, access to their data currently published online, and also access to those not yet regularly published on the web. At a later stage data exchange standards such as WaterML2.0 will be implemented. The project will also perform pan-Arctic hydrological modelling (geo-statistical, deterministic and probabilistic methods) for the assessment and integration of observational and modelled data to improve estimates of ungauged discharge and the overall estimates of freshwater flux to the Arctic Ocean, as well as understanding of hydrological processes.

  1. Oceanic spawning ecology of freshwater eels in the western North Pacific

    PubMed Central

    Tsukamoto, Katsumi; Chow, Seinen; Otake, Tsuguo; Kurogi, Hiroaki; Mochioka, Noritaka; Miller, Michael J.; Aoyama, Jun; Kimura, Shingo; Watanabe, Shun; Yoshinaga, Tatsuki; Shinoda, Akira; Kuroki, Mari; Oya, Machiko; Watanabe, Tomowo; Hata, Kazuhiro; Ijiri, Shigeho; Kazeto, Yukinori; Nomura, Kazuharu; Tanaka, Hideki

    2011-01-01

    The natural reproductive ecology of freshwater eels remained a mystery even after some of their offshore spawning areas were discovered approximately 100 years ago. In this study, we investigate the spawning ecology of freshwater eels for the first time using collections of eggs, larvae and spawning-condition adults of two species in their shared spawning area in the Pacific. Ovaries of female Japanese eel and giant mottled eel adults were polycyclic, suggesting that freshwater eels can spawn more than once during a spawning season. The first collection of Japanese eel eggs near the West Mariana Ridge where adults and newly hatched larvae were also caught shows that spawning occurs during new moon periods throughout the spawning season. The depths where adults and newly hatched larvae were captured indicate that spawning occurs in shallower layers of 150200 m and not at great depths. This type of spawning may reduce predation and facilitate reproductive success. PMID:21285957

  2. Carbon export associated with free-drifting icebergs in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Smith, K. L., Jr.; Sherman, A. D.; Shaw, T. J.; Murray, A. E.; Vernet, M.; Cefarelli, A. O.

    2011-06-01

    Enrichment of the pelagic ecosystem associated with the proliferation of free-drifting icebergs prompts questions about increased productivity and the export flux of organic carbon to the deep ocean with continued climate warming. Lagrangian Sediment Traps (LST) were deployed autonomously beneath a large tabular, free-drifting iceberg (C-18a) in the NW Weddell Sea during March and April 2009 to collect sinking particles at a depth of 600 m. Three LST deployments associated with C-18a, within a 30-km radius, collected sinking diatom frustules, dominated by Corethron pennatum and Fragilariopsis nana, euphausiid fragments, crustacean and fish fecal material, detrital aggregates and mineral grains. One LST deployment at a "control" site 74 km away in open water devoid of icebergs collected diatom frustules, euphausiid molts, crustacean fecal material and detrital aggregates. Phytoplankton abundance, microbial abundance and biomass were significantly higher in the LST samples than in open-water collections at 500 m depth. The mean mass flux and organic carbon flux associated with iceberg C-18a were twice as high, 124 mg m -2 d -1 and 5.6 mg C org m -2 d -1, respectively, than at the control site. A similar trend was observed in C org/ 234Th activity, being highest near C-18a and lowest at the control site. Extrapolation of the area of enrichment to 30 km radius around C-18a, 2826 km 2, produces an estimated mass flux of 350 tons d -1 and carbon flux of 15.8 tons C org d -1. Five similar sized icebergs to C-18a were identified in satellite images in a surrounding 47,636 km 2 area at the same time of sampling. Assuming a 30-km radius as the area of influence around each of these five icebergs, 46% of the total area would be enhanced with an export flux at 600 m of 122.4 tons C org d -1. The large numbers of smaller icebergs identified visually in this area would only increase this area of influence. Icebergs serve as areas of local enrichment and with increased proliferation, must be considered in the cycling of carbon in the Southern Ocean.

  3. Silicon pool dynamics and biogenic silica export in the Southern Ocean, inferred from Si-isotopes

    NASA Astrophysics Data System (ADS)

    Fripiat, F.; Cavagna, A.-J.; Dehairs, F.; Speich, S.; Andr, L.; Cardinal, D.

    2011-03-01

    Water column silicon isotopic signatures (?30Si) of silicic acid (Si(OH)4) in the Southern Ocean were measured along a meridional transect from South Africa (Subtropical Zone) down to 57 S (northern Weddell Gyre). These data are the first reported for a summer transect across the whole Antarctic Circumpolar Current (ACC). ?30Si variations are large in the upper 1000 m, reflecting the effect of the silica pump superimposed upon meridional transfer across the ACC: the transport of Antarctic surface waters northward by a net Ekman drift and their convergence and mixing with warmer upper-ocean Si-depleted waters to the north. Using Si isotopic signatures, we determined different mixing interfaces between ACC water masses: the Antarctic Surface Water (AASW), the Antarctic Intermediate Water (AAIW), and the thermoclines in the low latitude areas. The residual silicic acid concentrations of end-members control the ?30Si alteration of the mixing products. With the exception of AASW, all mixing interfaces have a highly Si-depleted mixed layer end-member. These processes deplete the silicic acid AASW concentration across the different interfaces northward without significantly changing the AASW ?30Si. By comparing our new results with a previous study in the Australian sector we show that during the circumpolar transport of the ACC eastward, there is a slight but significant Si-isotopic lightening of the silicic acid pools from the Atlantic to the Australian sectors. This results either from the dissolution of biogenic silica in the deeper layers and/or from an isopycnal mixing with the deep water masses in the different oceanic basins: North Atlantic Deep Water in the Atlantic, and Indian Ocean deep water in the Indo-Australian sector. This eastward lightening is further transmitted to the subsurface waters, representing mixing interfaces between the surface and deeper layers. Using the Si-isotopic constraint, we estimate for the Greenwich Meridian a net biogenic silica production which should be representative of the annual export, at 4.5 1.1 and 1.5 0.4 mol Si m-2 for the Antarctic Zone and Polar Front Zone, respectively, in agreement with previous estimations. The summertime Si-supply into the mixed layer via vertical mixing was also assessed at 1.5 0.4 and 0.1 0.5 mol Si m-2, respectively.

  4. Silicon pool dynamics and biogenic silica export in the Southern Ocean inferred from Si-isotopes

    NASA Astrophysics Data System (ADS)

    Fripiat, F.; Cavagna, A.-J.; Dehairs, F.; Speich, S.; Andr, L.; Cardinal, D.

    2011-09-01

    Silicon isotopic signatures (?30Si) of water column silicic acid (Si(OH)4) were measured in the Southern Ocean, along a meridional transect from South Africa (Subtropical Zone) down to 57 S (northern Weddell Gyre). This provides the first reported data of a summer transect across the whole Antarctic Circumpolar Current (ACC). ?30Si variations are large in the upper 1000 m, reflecting the effect of the silica pump superimposed upon meridional water transfer across the ACC: the transport of Antarctic surface waters northward by a net Ekman drift and their convergence and mixing with warmer upper-ocean Si-depleted waters to the north. Using Si isotopic signatures, we determine different mixing interfaces: the Antarctic Surface Water (AASW), the Antarctic Intermediate Water (AAIW), and thermoclines in the low latitude areas. The residual silicic acid concentrations of end-members control the ?30Si alteration of the mixing products and with the exception of AASW, all mixing interfaces have a highly Si-depleted mixed layer end-member. These processes deplete the silicic acid AASW concentration northward, across the different interfaces, without significantly changing the AASW ?30Si composition. By comparing our new results with a previous study in the Australian sector we show that during the circumpolar transport of the ACC eastward, the ?30Si composition of the silicic acid pools is getting slightly, but significantly lighter from the Atlantic to the Australian sectors. This results either from the dissolution of biogenic silica in the deeper layers and/or from an isopycnal mixing with the deep water masses in the different oceanic basins: North Atlantic Deep Water in the Atlantic, and Indian Ocean deep water in the Indo-Australian sector. This isotopic trend is further transmitted to the subsurface waters, representing mixing interfaces between the surface and deeper layers. Through the use of ?30Si constraints, net biogenic silica production (representative of annual export), at the Greenwich Meridian is estimated to be 5.2 1.3 and 1.1 0.3 mol Si m-2 for the Antarctic Zone and Polar Front Zone, respectively. This is in good agreement with previous estimations. Furthermore, summertime Si-supply into the mixed layer of both zones, via vertical mixing, is estimated to be 1.6 0.4 and 0.1 0.5 mol Si m-2, respectively.

  5. Millennial-scale variability in dust deposition, marine export production, and nutrient consumption in the glacial subantarctic ocean (Invited)

    NASA Astrophysics Data System (ADS)

    Martinez-Garcia, A.; Sigman, D. M.; Anderson, R. F.; Ren, H. A.; Hodell, D. A.; Straub, M.; Jaccard, S.; Eglinton, T. I.; Haug, G. H.

    2013-12-01

    Based on the limitation of modern Southern Ocean phytoplankton by iron and the evidence of higher iron-bearing dust fluxes to the ocean during ice ages, it has been proposed that iron fertilization of Southern Ocean phytoplankton contributed to the reduction in atmospheric CO2 during ice ages. In the Subantarctic zone of the Atlantic Southern Ocean, glacial increases in dust flux and export production have been documented, supporting the iron fertilization hypothesis. However, these observations could be interpreted alternatively as resulting from the equatorward migration of Southern Ocean fronts during ice ages if the observed productivity rise was not accompanied by an increase in major nutrient consumption. Here, new 230Th-normalized lithogenic and opal fluxes are combined with high-resolution biomarker measurements to reconstruct millennial-scale changes in dust deposition and marine export production in the subantarctic Atlantic over the last glacial cycle. In the same record foraminifera-bound nitrogen isotopes are used to reconstruct ice age changes in surface nitrate utilization, providing a comprehensive test of the iron fertilization hypothesis. Elevation in foraminifera-bound ?15N, indicating more complete nitrate consumption, coincides with times of surface cooling and greater dust flux and export production. These observations indicate that the ice age Subantarctic was characterized by iron fertilized phytoplankton growth. The resulting strengthening of the Southern Ocean's biological pump can explain the ~40 ppm lowering of CO2 that characterizes the transitions from mid-climate states to full ice age conditions as well as the millennial-scale atmospheric CO2 fluctuations observed within the last ice age

  6. An Ice-Tethered Instrument for Sustained Observation of Arctic Upper-Ocean Freshwater and Heat Content Variability

    NASA Astrophysics Data System (ADS)

    Toole, J. M.; Proshutinsky, A.; Krishfield, R. A.; Dohherty, K. W.

    2003-12-01

    To address the Arctic gap in the global ocean observing system, we are developing an expendable, ice-tethered instrument capable of making long-term observations of freshwater and heat content variability beneath the ice pack. The system will consist of a small surface package that will support a weighted tether extending down 500 or more meters into the water column along which a variant of the now-operational Moored Profiler instrument will travel. Conductivity-Temperature-Depth data from the Profiler will be transmitted to the surface unit via an inductive modem, be combined with any additional sensor data (such as atmospheric pressure and temperature) and relayed to shore using a satellite data telemetry unit. We envision a loose array of these Ice-Tethered Profilers repeatedly sampling the thermohaline properties of the upper ocean below the perennial ice pack at daily to weekly time scale. Beyond estimating vertically-integrated quantities such as freshwater anomalies, the better-than 1-m-vertical-resolution data will also be valuable for documenting and assessing double-diffusive layering, thermohaline intrusions and mesoscale eddies, all possibly important to the evolution of the Arctic ice-ocean system. Multi-year lifetime and modest cost will permit basin-scale coverage (about 20 or more systems) to be maintained through regular seeding of replacement units as necessary, similar to the surface ice buoys (measuring sea ice drift, sea level atmospheric pressure, and 2-meter air temperature) of the International Arctic Buoy Program (IABP). Operationally, the array will serve as the Arctic analogue of the ARGO float program now being initiated at lower latitudes. Further information on the Ice-Tethered Profiler system is available at http://ioeb.whoi.edu/itp.

  7. Dominant eukaryotic export production during ocean anoxic events reflects the importance of recycled NH4+.

    PubMed

    Higgins, Meytal B; Robinson, Rebecca S; Husson, Jonathan M; Carter, Susan J; Pearson, Ann

    2012-02-14

    The Mesozoic is marked by several widespread occurrences of intense organic matter burial. Sediments from the largest of these events, the Cenomanian-Turonian Oceanic Anoxic Event (OAE 2) are characterized by lower nitrogen isotope ratios than are seen in modern marine settings. It has remained a challenge to describe a nitrogen cycle that could achieve such isotopic depletion. Here we use nitrogen-isotope ratios of porphyrins to show that eukaryotes contributed the quantitative majority of export production throughout OAE 2, whereas cyanobacteria contributed on average approximately 20%. Such data require that any explanation for the OAE nitrogen cycle and its isotopic values be consistent with a eukaryote-dominated ecosystem. Our results agree with models that suggest the OAEs were high-productivity events, supported by vigorous upwelling. Upwelling of anoxic deep waters would have supplied reduced N species (i.e., NH(4)(+)) to primary producers. We propose that new production during OAE 2 primarily was driven by direct NH(4)(+)-assimilation supplemented by diazotrophy, whereas chemocline denitrification and anammox quantitatively consumed NO(3)(−) and NO(2)(−). A marine nitrogen reservoir dominated by NH(4)(+), in combination with known kinetic isotope effects, could lead to eukaryotic biomass depleted in (15)N. PMID:22315397

  8. Dominant eukaryotic export production during ocean anoxic events reflects the importance of recycled NH4+

    PubMed Central

    Higgins, Meytal B.; Robinson, Rebecca S.; Husson, Jonathan M.; Carter, Susan J.; Pearson, Ann

    2012-01-01

    The Mesozoic is marked by several widespread occurrences of intense organic matter burial. Sediments from the largest of these events, the CenomanianTuronian Oceanic Anoxic Event (OAE 2) are characterized by lower nitrogen isotope ratios than are seen in modern marine settings. It has remained a challenge to describe a nitrogen cycle that could achieve such isotopic depletion. Here we use nitrogen-isotope ratios of porphyrins to show that eukaryotes contributed the quantitative majority of export production throughout OAE 2, whereas cyanobacteria contributed on average approximately 20%. Such data require that any explanation for the OAE nitrogen cycle and its isotopic values be consistent with a eukaryote-dominated ecosystem. Our results agree with models that suggest the OAEs were high-productivity events, supported by vigorous upwelling. Upwelling of anoxic deep waters would have supplied reduced N species (i.e., ) to primary producers. We propose that new production during OAE 2 primarily was driven by direct -assimilation supplemented by diazotrophy, whereas chemocline denitrification and anammox quantitatively consumed and . A marine nitrogen reservoir dominated by , in combination with known kinetic isotope effects, could lead to eukaryotic biomass depleted in 15N. PMID:22315397

  9. Trace element behaviour at cold seeps and the potential export of dissolved iron to the ocean

    NASA Astrophysics Data System (ADS)

    Lemaitre, Nolwenn; Bayon, Germain; Ondras, Hlne; Caprais, Jean-Claude; Freslon, Nicolas; Bollinger, Claire; Rouget, Marie-Laure; de Prunel, Alexis; Ruffine, Livio; Olu-Le Roy, Karine; Sarthou, Graldine

    2014-10-01

    Seawater samples were collected by submersible above methane seeps in the Gulf of Guinea (Regab and Baboon pockmarks) in order to investigate the behaviour of iron (Fe), manganese (Mn) and rare earth elements (REE) during fluid seepage. Our aim was to determine whether cold seeps may represent potential sources of dissolved chemical species to the ocean. Dissolved (<0.45 ?m filtered samples) and total dissolvable (unfiltered samples) concentrations were determined over ?50 m long vertical transects above the seafloor and at various discrete locations within the pockmarks. We show that substantial amounts of Fe and Mn are released into seawater during seepage of methane-rich fluids. Mn is exported almost quantitatively in the dissolved form (more than 90% of total Mn; mean MnDISS?1211 nmol/kg). Although a significant fraction of Fe is bound to particulate phases, the dissolved iron pool still accounts on average for approximately 20 percent of total iron flux at vent sites (mean FeDISS?2211 nmol/kg). This dissolved Fe fraction also appears to remain stable in the water column. In contrast, there was no evidence for any significant benthic fluxes of pore water REE associated with fluid seepage at the studied sites. Overall, our results point towards distinct trace element behaviour during fluid seepage, with potential implications for the marine geochemical budget. The absence of any dissolved REE enrichments in bottom waters clearly indicates effective removal in sub-surface sediments. Most likely, precipitation of authigenic mineral phases at cold seeps (i.e. carbonates) represents a net sink for these elements. While Mn appears to behave near-conservatively during fluid seepage, the observed relative stability of dissolved Fe in the water column above seepage sites could be explained by complexation with strong organic ligands and/or the presence of Fe-bearing sulfide nanoparticles, as reported previously for submarine hydrothermal systems. Considering the ubiquitous occurrence of methane vents at ocean margins, cold seeps could represent a previously unsuspected source of dissolved Fe to the deep ocean.

  10. The alpha/beta ocean distinction: A perspective on freshwater fluxes, convection, nutrients and productivity in high-latitude seas

    NASA Astrophysics Data System (ADS)

    Carmack, Eddy C.

    2007-11-01

    Stratification is perhaps the most important attribute of oceans with regards to climate and biology. Two simple aspects of the ocean's climate system appear to have a surprisingly important role in transforming waters that feed the global thermohaline circulation, dominating patterns of biogeochemical flux and establishing macroecological domains. First, largely because of meridional distillation (mainly due to the atmospheric transport of freshwater across the Isthmus of Panama) the North Pacific is fresher than the North Atlantic. Second, largely because of zonal distillation (e.g., warming and evaporation at low latitudes and poleward transport of latent heat and moisture by the atmosphere) the upper layers of subtropical seas are permanently stratified by temperature ( NT2= g?d T/d z>0; here called alpha oceans), while the upper layers of high-latitude seas are permanently stratified by salinity ( NS2= g?d S/d z>0; here called beta oceans). The physical basis for the boundary separating alpha and beta oceans is unclear, but may lie in the thermodynamical equations published by Fofonoff [1961. Energy transformations in the sea. Fisheries Research Board of Canada, Report Series 109, 82pp]. Nevertheless, it is clear that the resulting thermohaline distributions establish a 'downhill journey' of low-salinity (and nutrient-rich) waters from the North Pacific to the Arctic and then into the North Atlantic. The Arctic Oceanitselfacts a double estuary, whereby waters entering from the North Atlantic become either denser through cooling (negative estuary) or lighter by freshening (positive estuary) as they circulate within the basin and then return to the North Atlantic as a variety of components of the ocean's conveyor. Intermediate and deep waters generally form within cyclonic beta oceans in close proximity to alphas systems. Similar patterns of stratification, nutrients and biogeographical boundaries persist in the Southern Hemisphere. It is thus argued that this simple distinctionalpha versus beta oceansprovides a broad, conceptual framework for simple interpretation of key physical and biological processes and rates, including the impacts of climate variability.

  11. Carbon export in the naturally iron-fertilized Kerguelen area of the Southern Ocean based on the 234Th approach

    NASA Astrophysics Data System (ADS)

    Planchon, F.; Ballas, D.; Cavagna, A.-J.; Bowie, A. R.; Davies, D.; Trull, T.; Laurenceau-Cornec, E. C.; Van Der Merwe, P.; Dehairs, F.

    2015-06-01

    This study examined upper-ocean particulate organic carbon (POC) export using the 234Th approach as part of the second KErguelen Ocean and Plateau compared Study expedition (KEOPS2). Our aim was to characterize the spatial and the temporal variability of POC export during austral spring (October-November 2011) in the Fe-fertilized area of the Kerguelen Plateau region. POC export fluxes were estimated at high productivity sites over and downstream of the plateau and compared to a high-nutrient low-chlorophyll (HNLC) area upstream of the plateau in order to assess the impact of iron-induced productivity on the vertical export of carbon. Deficits in 234Th activities were observed at all stations in surface waters, indicating early scavenging by particles in austral spring. 234Th export was lowest at the reference station R-2 and highest in the recirculation region (E stations) where a pseudo-Lagrangian survey was conducted. In comparison 234Th export over the central plateau and north of the polar front (PF) was relatively limited throughout the survey. However, the 234Th results support that Fe fertilization increased particle export in all iron-fertilized waters. The impact was greatest in the recirculation feature (3-4 fold at 200 m depth, relative to the reference station), but more moderate over the central Kerguelen Plateau and in the northern plume of the Kerguelen bloom (~2-fold at 200 m depth). The C : Th ratio of large (>53 μm) potentially sinking particles collected via sequential filtration using in situ pumping (ISP) systems was used to convert the 234Th flux into a POC export flux. The C : Th ratios of sinking particles were highly variable (3.1 ± 0.1 to 10.5 ± 0.2 μmol dpm-1) with no clear site-related trend, despite the variety of ecosystem responses in the fertilized regions. C : Th ratios showed a decreasing trend between 100 and 200 m depth suggesting preferential carbon loss relative to 234Th possibly due to heterotrophic degradation and/or grazing activity. C : Th ratios of sinking particles sampled with drifting sediment traps in most cases showed very good agreement with ratios for particles collected via ISP deployments (>53 μm particles). Carbon export production varied between 3.5 ± 0.9 and 11.8 ± 1.3 mmol m-2 d-1 from the upper 100 m and between 1.8 ± 0.9 and 8.2 ± 0.9 mmol m-2 d-1 from the upper 200 m. The highest export production was found inside the PF meander with a range of 5.3 ± 1.0 to 11.8 ± 1.1 mmol m-2 d-1 over the 19-day survey period. The impact of Fe fertilization is highest inside the PF meander with 2.9-4.5-fold higher carbon flux at 200 m depth in comparison to the HNLC control station. The impact of Fe fertilization was significantly less over the central plateau (stations A3 and E-4W) and in the northern branch of the bloom (station F-L) with 1.6-2.0-fold higher carbon flux compared to the reference station R. Export efficiencies (ratio of export to primary production and ratio of export to new production) were particularly variable with relatively high values in the recirculation feature (6 to 27 %, respectively) and low values (1 to 5 %, respectively) over the central plateau (station A3) and north of the PF (station F-L), indicating spring biomass accumulation. Comparison with KEOPS1 results indicated that carbon export production is much lower during the onset of the bloom in austral spring than during the peak and declining phases in late summer.

  12. Export fluxes in a naturally iron-fertilized area of the Southern Ocean - Part 1: Seasonal dynamics of particulate organic carbon export from a moored sediment trap

    NASA Astrophysics Data System (ADS)

    Rembauville, M.; Salter, I.; Leblond, N.; Gueneugues, A.; Blain, S.

    2015-06-01

    A sediment trap moored in the naturally iron-fertilized Kerguelen Plateau in the Southern Ocean provided an annual record of particulate organic carbon and nitrogen fluxes at 289 m. At the trap deployment depth, current speeds were typically low (~ 10 cm s-1) and primarily tidal-driven (M2 tidal component). Although advection was weak, the sediment trap may have been subject to hydrodynamical and biological (swimmer feeding on trap funnel) biases. Particulate organic carbon (POC) flux was generally low (< 0.5 mmol m-2 d-1), although two episodic export events (< 14 days) of 1.5 mmol m-2 d-1 were recorded. These increases in flux occurred with a 1-month time lag from peaks in surface chlorophyll and together accounted for approximately 40% of the annual flux budget. The annual POC flux of 98.2 4.4 mmol m-2 yr-1 was low considering the shallow deployment depth but comparable to independent estimates made at similar depths (~ 300 m) over the plateau, and to deep-ocean (> 2 km) fluxes measured from similarly productive iron-fertilized blooms. Although undertrapping cannot be excluded in shallow moored sediment trap deployment, we hypothesize that grazing pressure, including mesozooplankton and mesopelagic fishes, may be responsible for the low POC flux beneath the base of the winter mixed layer. The importance of plankton community structure in controlling the temporal variability of export fluxes is addressed in a companion paper.

  13. Pacific Ocean surface freshwater variability underneath the double ITCZ as seen by satellite sea surface salinity retrievals

    NASA Astrophysics Data System (ADS)

    Sena Martins, Meike; Stammer, Detlef

    2015-08-01

    The salinity budget of the upper tropical Pacific Ocean underneath the double Intertropical Convergence Zone (ITCZ) is studied using the Soil Moisture and Ocean Salinity (SMOS) and Aquarius surface salinity observations as well as in situ salinity measurements. In this shallow mixed layer region of the ocean, precipitation effects on the near-surface salinity budget are large, typically leading to a band of fresh sea surface salinity (SSS) between March and June. The role of precipitation during the freshening period is documented here through a direct correlation between the SMOS SSS fields and the monthly accumulated precipitation. During the same period, the mixed layer salinity budget is impacted by advection, which, based on in situ observations, is found to be another important mechanism for the evolution of the near-surface salinity as documented through a connection between the north equatorial eastern Pacific Fresh water pool and this south equatorial freshwater pattern in boreal spring. However, given the information at hand, the near-surface salinity budget cannot be closed, suggesting that other processes are important too, such as nonlinear effects, mixing, and entrainment.

  14. Influence of freshwater flow, ocean exchange, and seasonal cycles on phytoplankton nutrient dynamics in a temporarily open estuary

    NASA Astrophysics Data System (ADS)

    Gobler, Christopher J.; Cullison, Leah A.; Koch, Florian; Harder, Timothy M.; Krause, Jeffrey W.

    2005-10-01

    Mecox Bay is a shallow, closed embayment, located on the south shore of Long Island, NY, which has an inlet that is periodically opened by natural and anthropogenic processes, allowing for tidal exchange with the coastal Atlantic Ocean. The aim of this study was to characterize the phytoplankton community and water chemistry of Mecox Bay, while assessing the impact of inlet openings and freshwater flow on these characteristics. Results indicated that groundwater and tributaries entering Mecox were an important source of nitrogen (N) to the bay, being enriched in dissolved inorganic nitrogen (DIN = 140 20 ?M). Inlet openings yielded increased salinity and chlorophyll a levels, but decreased depths and diatom densities in Mecox Bay. Other parameters, such as nutrient concentrations (N, P), pico- and nanophytoplankton densities, and the nutrient limitation of phytoplankton communities were more strongly influenced by seasonal changes associated with temperature. Dissolved inorganic nitrogen-to-phosphorus ratios decreased from above 100 during winter to below one during summer, as concentrations of DIN and freshwater flow rates in Mecox Bay declined and DIP levels concurrently increased. In concert with changes in the nutrient regime, field experiments indicated that growth rates of the phytoplankton community in Mecox Bay shifted from P-limited during winter and spring to N-limited during summer and fall. Finally, the abundance of phytoplankton (mean annual chlorophyll a concentration 10 ?g L -1) and the temporarily closed nature of Mecox Bay may both contribute toward enhanced secondary productivity of resident shellfish populations.

  15. The freshwater lens of Benjamín Aceval, Chaco, Paraguay: a terrestrial analogue of an oceanic island lens

    NASA Astrophysics Data System (ADS)

    Houben, Georg; Noell, Ursula; Vassolo, Sara; Grissemann, Christoph; Geyh, Mebus; Stadler, Susanne; Dose, Eduardo J.; Vera, Sofia

    2014-12-01

    The occurrence of a freshwater lens in the Paraguayan Chaco, 900 km away from the ocean, is reported. It is located underneath sandstone hills, surrounded by lowlands with predominantly saline groundwater. Its geometry was delineated using geoelectrical and electromagnetic investigations. The unusual height of the fresh groundwater level can be attributed to the presence of a confining layer at depth. The lens receives its recharge exclusively from rainfall during the hot and humid summer months. It predominantly contains water predating the atmospheric atomic bomb tests, some of it probably up to a thousand or more years old. The water balance shows that extraction currently does not exceed recharge in normal years. However, the available volume of groundwater leaves little room for a further increase of extraction in the future. Recharge is augmented by return flow from thousands of latrines and cess pits, and this has lead to widespread contamination of the groundwater by faecal bacteria.

  16. Southern-ocean and glaciogenic nutrients control diatom export production on the Chile margin

    NASA Astrophysics Data System (ADS)

    Chase, Zanna; McManus, James; Mix, Alan C.; Muratli, Jesse

    2014-09-01

    Biogenic particle flux was reconstructed using 230-Thorium normalization at two sites on the southern Chile margin. ODP Site 1233 at 41°S, 838 m depth, is at the southern limit of the Peru-Chile upwelling system, where the northern extent of the Antarctic Circumpolar Current impinges on the South American continental margin. ODP Site 1234, at 36°S, 1014 m depth, is located within the core of the coastal upwelling system near the mouths of the Bio Bio and Itata Rivers. At 41°S, opal, lithogenic and carbonate fluxes are greatest during the Last Glacial interval (26-20 ka), carbonate has a secondary peak during the mid Holocene (˜8 ka) and organic carbon fluxes increase slightly from 17 ka to the present. At 36°S, large lithogenic fluxes are observed both during the Last Glacial interval and the Holocene, and a maximum in organic carbon flux is observed during the late Holocene (˜5 ka) without an accompanying peak in opal flux. These reconstructed fluxes at 36°S and 41°S fit within a larger latitudinal pattern of a poleward increase in the magnitude of opal flux during the glacial period. The pattern of normalized opal flux, opal mass accumulation rate and opal:carbonate ratios is consistent with either i) enhanced supply of Si from the Southern Ocean, as proposed by the Silicic Acid Leakage Hypothesis or ii) enhanced Si and Fe delivery from land, driven by glacial erosion. The pattern of reconstructed export production supports our view that the appearance of more reducing conditions in the sediments upon deglaciation was most likely driven by decreased ventilation, rather than increased local productivity.

  17. The relative contribution of fast and slow sinking particles to ocean carbon export

    NASA Astrophysics Data System (ADS)

    Riley, J. S.; Sanders, R.; Marsay, C.; Le Moigne, F. A. C.; Achterberg, E. P.; Poulton, A. J.

    2012-03-01

    Particulate organic carbon (POC) generated by primary production and exported to depth, is an important pathway for carbon transfer to the abyss, where it is stored over climatically significant timescales. These processes constitute the biological carbon pump. A spectrum of particulate sinking velocities exists throughout the water column, however numerical models often simplify this spectrum into suspended, fast and slow sinking particles. Observational studies suggest the spectrum of sinking speeds in the ocean is strongly bimodal with >85% POC flux contained within two pools with sinking speeds of <10 m day-1 and >350 m day-1. We deployed a Marine Snow Catcher (MSC) to estimate the magnitudes of the suspended, fast and slow sinking pools and their fluxes at the Porcupine Abyssal Plain site (48N, 16.5W) in summer 2009. The POC concentrations and fluxes determined were 0.2 ?g C L-1 and 54 mg C m-2 day-1 for fast sinking particles, 5 ?g C L-1 and 92 mg C m-2 day-1 for slow sinking particles and 97 ?g C L-1 for suspended particles. Our flux estimates were comparable with radiochemical tracer methods and neutrally buoyant sediment traps. Our observations imply: (1) biomineralising protists, on occasion, act as nucleation points for aggregate formation and accelerate particle sinking; (2) fast sinking particles alone were sufficient to explain the abyssal POC flux; and (3) there is no evidence for ballasting of the slow sinking flux and the slow sinking particles were probably entirely remineralised in the twilight zone.

  18. Saharan Dust Export towards the Caribbean: Transport, Mixing and Deposition Processes over the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Heinold, Bernd; Schepanski, Kerstin; Haarig, Moritz; Ansmann, Albert; Gro, Silke; Schfler, Andreas; Weinzierl, Bernadett; Tegen, Ina

    2015-04-01

    Large amounts of Saharan dust are carried towards the Caribbean within the Saharan Air Layer (SAL), with maximum transport in late boreal spring and early summer. During long-range transport, the dust particles are transformed by aging and mixing, which may have significant but as yet unquantified effects on the dust impact on radiation, cloud properties, and the biogeochemical processes of ecosystems. Here, we investigate the long-range transport of Saharan dust across the Atlantic Ocean by means of transport modelling that has been performed within the framework of the SALTRACE (Saharan Aerosol Long-Range Transport and Aerosol-Cloud Interaction Experiment) project. The emission, transport, dry and wet deposition of Saharan dust as well as the effect of dust radiative forcing are simulated with the regional model COSMO-MUSCAT. The model results are evaluated against the various ground and airborne observations from the SALTRACE field measurements at Barbados Island in June and July 2013. The dust simulations, in turn, help to interpret the observations, in particular from a Lagrangian flight experiment, by providing a spatiotemporal context. Specifically, this study addresses the questions of (a) how the Saharan dust export towards the Caribbean is influenced by the atmospheric circulation over West Africa, (b) which role the different removal and mixing processes play during long-range transport, and (c) what is the impact of dust forcing on the vertical structure of the SAL? In addition, the Saharan dust simulations with COSMO-MUSCAT are combined with trajectory analysis to study particle aging and dust-cloud interactions.

  19. Kara Sea freshwater transport through Vilkitsky Strait: Variability, forcing, and further pathways toward the western Arctic Ocean from a model and observations

    NASA Astrophysics Data System (ADS)

    Janout, Markus A.; Aksenov, Yevgeny; Hlemann, Jens A.; Rabe, Benjamin; Schauer, Ursula; Polyakov, Igor V.; Bacon, Sheldon; Coward, Andrew C.; Karcher, Michael; Lenn, Yueng-Djern; Kassens, Heidemarie; Timokhov, Leonid

    2015-07-01

    Siberian river water is a first-order contribution to the Arctic freshwater budget, with the Ob, Yenisey, and Lena supplying nearly half of the total surface freshwater flux. However, few details are known regarding where, when, and how the freshwater transverses the vast Siberian shelf seas. This paper investigates the mechanism, variability, and pathways of the fresh Kara Sea outflow through Vilkitsky Strait toward the Laptev Sea. We utilize a high-resolution ocean model and recent shipboard observations to characterize the freshwater-laden Vilkitsky Strait Current (VSC), and shed new light on the little-studied region between the Kara and Laptev Seas, characterized by harsh ice conditions, contrasting water masses, straits, and a large submarine canyon. The VSC is 10-20 km wide, surface intensified, and varies seasonally (maximum from August to March) and interannually. Average freshwater (volume) transport is 500 120 km3 a-1 (0.53 0.08 Sv), with a baroclinic flow contribution of 50-90%. Interannual transport variability is explained by a storage-release mechanism, where blocking-favorable summer winds hamper the outflow and cause accumulation of freshwater in the Kara Sea. The year following a blocking event is characterized by enhanced transports driven by a baroclinic flow along the coast that is set up by increased freshwater volumes. Eventually, the VSC merges with a slope current and provides a major pathway for Eurasian river water toward the western Arctic along the Eurasian continental slope. Kara (and Laptev) Sea freshwater transport is not correlated with the Arctic Oscillation, but rather driven by regional summer pressure patterns.

  20. Diatom resting spore ecology drives enhanced carbon export from a naturally iron-fertilized bloom in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Salter, Ian; Kemp, Alan E. S.; Moore, C. Mark; Lampitt, Richard S.; Wolff, George A.; Holtvoeth, Jens

    2012-03-01

    Southern Ocean Island systems sustain phytoplankton blooms induced by natural iron fertilization that are important for the uptake of atmospheric carbon dioxide and serve as analogues for past and future climate change. We present data on diatom flux assemblages and the biogeochemical properties of sinking particles to explain the enhanced particulate organic carbon (POC) export fluxes observed in response to natural iron supply in the Crozet Islands region (CROZeX). Moored deep-ocean sediment traps (>2000 m) were located beneath a naturally fertilized island bloom and beneath an adjacent High Nutrient Low Chlorophyll (HNLC) control site. Deep-ocean carbon flux from the naturally-fertilized bloom area was tightly correlated (R = 0.83, n = 12, P < 0.0006) with the resting spore flux of a single island-associated diatom species,Eucampia antarctica var. antarctica. The unusually well preserved state of the Eucampia-associated carbon flux, determined by amino acid studies of organic matter degradation, was likely influenced by their ecology, since diatom resting spores are adapted to settle rapidly out of the surface ocean preserving viable cells. The naturally fertilized bloom enhanced carbon flux and the resulting Si/C and Si/N ratios were 2.0-3.4-fold and 2.2-3.5-fold lower than those measured in the adjacent HNLC control area. The enhanced carbon export and distinctive stoichiometry observed in naturally fertilized systems is therefore largely not attributable to iron relief of open ocean diatoms, but rather to the advection and growth of diatom species characteristic of island systems and the subsequent flux of resting spores. Carbon export estimates from current natural iron fertilization studies therefore represent a highly specific response of the island systems chosen as natural laboratories and may not be appropriate analogues for the larger Southern Ocean response. The broader implications of our results emphasize the role of phytoplankton diversity and ecology and highlight the need for a species-centered approach in order to understand the regulation of biogeochemical fluxes.

  1. Hydrography, oxygen saturation, suspended particulate matter, and chlorophyll- a fluorescence in an oceanic region under freshwater influence

    NASA Astrophysics Data System (ADS)

    Signoret, Martha; Monreal-Gmez, Mara Adela; Aldeco, Javier; Salas-de-Len, David Alberto

    2006-08-01

    During the northern hemisphere summer of 1999, we analyzed the hydrography, oxygen saturation, suspended particulate matter, and chlorophyll- a fluorescence of the Southern Gulf of Mexico, an oceanic region under the influence of freshwater from the Grijalva-Usumacinta Rivers system. This rivers system induces thermal and haline fronts within the Southern Gulf, with surface temperature and salinity increasing offshore. A westward shelf circulation is inferred from the tilting of isopycnes and cold water on the bottom of the shelf break. Oxygen saturation shows low values in the region under freshwater influence. The composition of suspended particulate matter shows high variability, with the inorganic fraction dominant over the organic fraction. At the edge of the continental slope, the organic fraction is very high within the euphotic layer. The vertical distribution of chlorophyll- a fluorescence indicates different trophic conditions within the water column at three studied regions: the eastern shallow region, the middle shelf, and the continental slope. We found mesotrophic or eutrophic waters at the chlorophyll- a maximum level and oligotrophic waters at the background level. The behavior of the analyzed variables enables us to identify three ecological regions: (1) the inner shelf, where chlorophyll- a fluorescence increases near the seafloor, related to the thermocline; in this region the euphotic layer comprises the entire water column; (2) the middle shelf, with a sharp maximum of chlorophyll- a at mid-depths, strongly associated with the thermocline; and (3) the outer region above the continental slope that shows a deep-level chlorophyll- a maximum associated with low-light conditions. We propose that the vertical structure of chlorophyll- a fluorescence in the study area is dependant on thermal and light structures, and in some cases on the thermal and haline fronts associated with the river plumes, as well as on the regional circulation pattern.

  2. Carbon export in the naturally iron-fertilized Kerguelen area of the Southern Ocean based on the 234Th approach

    NASA Astrophysics Data System (ADS)

    Planchon, F.; Ballas, D.; Cavagna, A.-J.; Bowie, A. R.; Davies, D.; Trull, T.; Laurenceau, E.; Van Der Merwe, P.; Dehairs, F.

    2014-11-01

    The Kerguelen Plateau region in the Indian sector of the Southern Ocean supports annually a large-scale phytoplankton bloom which is naturally fertilized with iron. As part of the second KErguelen Ocean and Plateau compared Study expedition (KEOPS2) in austral spring (October-November 2011), we examined upper-ocean Particulate Organic Carbon (POC) export using the 234Th approach. We aimed at characterizing the spatial and the temporal variability of POC export production at high productivity sites over and downstream the Kerguelen plateau. Export production is compared to a High Nutrient Low Chlorophyll area upstream of the plateau in order to assess the impact of iron-induced productivity on the vertical export of carbon. Deficits in 234Th activities relative to its parent nuclide 238U were observed at all stations in surface waters, indicating that scavenging by particles occurred during the early stages of the phytoplankton bloom. 234Th export was lowest at reference station R-2 (412 ± 134 dpm m-2 d-1) and highest inside a~permanent meander of the Polar Front (PF) at stations E (1995 ± 176 dpm m-2 d-1, second visit E-3) where a detailed time series was obtained as part of a~pseudo-lagrangian study. 234Th export over the central plateau was relatively limited at station A3 early (776 ± 171 dpm m-2 d-1, first visit A3-1) and late in the survey (993 ± 223 dpm m-2 d-1, second visit A3-2), but it was higher at high biomass stations TNS-8 (1372 ± 255 dpm m-2 d-1) and E-4W (1068 ± 208 dpm m-2 d-1) in waters which could be considered as derived from plateau. Limited 234Th export of 973 ± 207 dpm m-2 d-1 was also found in the northern branch of the Kerguelen bloom located downstream of the island, north of the PF (station F-L). The 234Th results support that Fe fertilization increased particle export in all iron fertilized waters. The impact was greatest in the recirculation feature (3-4 fold at 200 m depth), but more moderate over the central Kerguelen plateau and in the northern plume of the Kerguelen bloom (∼2-fold at 200 m depth). The C : Th ratio of large (> 53 μm) potentially sinking particles collected via sequential filtration using in situ pumping (ISP) systems were used to convert the 234Th flux into a POC export flux. The C : Th ratios of sinking particles were highly variable (range: 3.1 ± 0.1-10.5 ± 0.2 μmol dpm-1) with no clear site related trend, despite the variety of ecosystem responses in the fertilized regions. C : Th ratios showed a decreasing trend between 100 and 200 m depth suggesting preferential loss of carbon relative to 234Th possibly due to heterotrophic degradation and/or grazing activity. Comparison of the C : Th ratios within sinking particles obtained with the drifting sediment traps showed in most cases very good agreement to those collected via ISP deployments (> 53 μm particles). Carbon export production varied between 3.5 ± 0.9 mmol m-2 d-1 and 11.8 ± 1.3 mmol m-2 d-1 from the upper 100 m and between 1.8 ± 0.9 mmol m-2 d-1 and 8.2 ± 0.9 mmol m-2 d-1 from the upper 200 m. Highest export production was found inside the PF meander with a range of 5.4 ± 0.7 mmol m-2 d-1 to 11.8 ± 1.1 mmol m-2 d-1 at 100 m depth decreasing to 5.3 ± 1.0 mmol m-2 d-1 to 8.2 ± 0.8 mmol m-2 d-1 at 200 m depth over the 19 day survey period. The impact of Fe fertilization is highest inside the PF meander with 2.9- up to 4.5-fold higher carbon flux at 200 m depth in comparison to the HNLC control station. The impact of Fe fertilization was significantly less over the central plateau (stations A3 and E-4W) and in the northern branch of the bloom (station F-L) with 1.6- up to 2.0-fold higher carbon flux compared to the reference station R. Export efficiencies (ratio of export to primary production) were particularly variable with relatively high values in the recirculation feature (6-27%) and low values (1-5%) over the central plateau (station A3) and north of the PF (station F-L) indicating spring biomass accumulation. Comparison with KEOPS1 results indicated that carbon export production is much lower during the onset of the bloom in austral spring in comparison to the peak and declining phase in late summer.

  3. Arctic Freshwater Fluxes and the Strength of the Conveyor Belt

    NASA Astrophysics Data System (ADS)

    Schlosser, P.; Newton, R.

    2006-12-01

    It is frequently argued that one of the major links between the Arctic and the lower latitudes is the influence of the freshwater export from high northern latitudes on the strength of the Meridional Overturning Circulation (MOC) or 'Global Ocean Conveyor Belt'. Specifically, it is often stated that a direct link exists between the flux of freshwater from the Arctic and volume transport of the Conveyor. In this contribution we examine the steady-state freshwater fluxes from the Arctic to the North Atlantic, as well as the expected increases of these fluxes as a consequence of projected warming scenarios. We will use these results to explore the likely response of the global conveyor to increased Arctic freshwater fluxes and discuss the implications of a slowing of the Conveyor for global atmospheric temperature fields.

  4. Recent Changes in Arctic Sea-Ice as a Component of the Arctic Freshwater System

    NASA Astrophysics Data System (ADS)

    Moritz, R. E.

    2005-12-01

    With a salinity typically one-tenth that of seawater, Arctic sea-ice can be an effective agent for the transport of freshwater within the Arctic, and for export from the Arctic to lower latitude. Large and persistent changes have occurred in the concentration, extent, thickness, motion and age of sea-ice during the era of good satellite observations, approximately 1970-2005. These changes are summarized and interpreted in terms of their relationships to the freshwater cycle of the Arctic, and the export of freshwater to the high latitude North Atlantic Ocean. Quantitative estimates of freshwater content and horizontal flux are updated using observations from the North Pole Environmental Observatory, 2001-2005.

  5. Composition of settling particles in the Southern Ocean and processes controlling seasonal variations of deep export production

    NASA Astrophysics Data System (ADS)

    Cardinal, Damien; Ameur, Khedidja; Closset, Ivia; Bray, Stephen; Trull, Thomas W.

    2014-05-01

    In order to understand the processes controlling the biological carbon pump and the efficiency of export production, we need time series in contrasted oceanic regions that fully describe seasonality. Due to strong logistic constraints, especially in the Southern Ocean, such data can only be obtained from above (satellite) or from below (sediment traps). In this study, settling particles of Subantarctic Zone (SAZ), Polar Front Zone (PFZ) and Antarctic Zone (AZ) along the CLIVAR-SR3 transect (140E, south to Tasmania) have been collected in sediment traps deployed at 1000, 2000 and 3800m (SAZ), 800 and 1500 m (PFZ) and 200 and 3700 m (AZ). In addition to the measurements of Particulate Organic Carbon, Particulate Inorganic Carbon, Biogenic silica we have measured particulate composition of some trace and major elements (Al, Ca, Fe, Ti, Ba, Sr, Mn, U, light Rare Earth Elements) by ICP-MS. When looking at correlations between elemental fluxes we show that there are generally different modes of variations. Surprisingly, those are not necessarily site-specific, i.e. different periods of SAZ and AZ traps can behave in a similar way, while they can be strongly decoupled at other periods. This is the case not only for biogenic elements (e.g. Ba, Ca, Sr) but also for elements usually representative of lithogenic particles (e.g., Al, Fe, Ti). More particularly Al vs. Fe fluxes appear to be strongly bimodal: Al fluxes are generally higher in northern traps while Fe fluxes are higher in AZ and PFZ traps; moreover single data points of both traps are distributed over two clear correlation lines, each one displaying little scattering. This suggests that the types of Fe- and/or Al- bearing particles vary more seasonally than spatially. In contrast, Ba fluxes, which are used in paleo-oceanography as a proxy of export production, are very similar to Ca fluxes, whatever the location. This suggests that carbonate productivity is more prone to deep carbon export compared to opal-dominated productivity probably as a result of higher mesopelagic C remineralisation efficiency reducing deep C export for the later. We will further discuss the implications of these results for our understanding of the element biogeochemical cycles in the Southern Ocean and their likely impact on surface productivity, ballast effect and carbon cycle.

  6. Freshwater and polynya components of the shelf-derived Arctic Ocean halocline in summer 2007 identified by stable oxygen isotopes

    NASA Astrophysics Data System (ADS)

    Bauch, D.; Rutgers van der Loeff, M.; Andersen, N.; Torres-Valdes, S.; Bakker, K.; Abrahamsen, E.

    2011-12-01

    With the aim of determining the origin of freshwater in the halocline, fractions of river water and sea-ice meltwater (or brine influence from sea-ice formation) in the upper 150 m were quantified by a combination of salinity and ?18O and nutrients in the Eurasian basins and the Makarov Basin. Our study indicates which layers of the Arctic Ocean halocline are primarily influenced by sea-ice formation in coastal polynyas and which are primarily influenced by sea-ice formation over the open ocean. With the ongoing changes in sea-ice coverage in the Arctic Ocean it can be expected that these processes will change in the immediate future and that the relative contributions to the halocline will change accordingly. Within the Eurasian Basin a west to east oriented front between net melting and production of sea-ice is observed. Outside the Atlantic regime dominated by net sea-ice melting, a pronounced layer influenced by brines released during sea-ice formation is present at about 30 to 50 m water depth with a maximum over the Lomonosov Ridge. The geographically distinct definition of this maximum demonstrates the rapid release and transport of signals from the shelf regions in discrete pulses within the Transpolar Drift. We use the ratio of sea-ice derived brine influence and river water to link the maximum in brine influence within the Transpolar Drift with a pulse of shelf waters from the Laptev Sea likely released in summer 2005. For a distinction of Atlantic and Pacific-derived contributions the initial phosphate corrected for mineralization with oxygen (PO*) and alternatively the nitrate to phosphate ratio (N/P) in each sample were used. While PO*-based assessments systematically underestimate the contribution of Pacific-derived waters, N/P-based calculations overestimate Pacific-derived waters within the Transpolar Drift due to denitrification in bottom sediments of the Laptev Sea. The extent of Pacific-derived water in the Arctic Ocean was approximately limited by the position of the Lomonosov Ridge in 2007. The ratio of sea-ice derived brine influence and river water is roughly constant within each layer of the Arctic Ocean halocline. The correlation between brine influence and river water reveals two clusters that can be assigned to the two main mechanisms of sea-ice formation within the Arctic Ocean. Over the open ocean or in polynyas at the continental slope sea-ice formation results in a linear correlation between brine influence and river water at salinities of ~ 32 to 34. In coastal polynyas in the shallow regions of the Laptev Sea and southern Kara Sea, sea-ice formation transports river water into the shelf's bottom layer due to the close proximity to the river mouths. This process results in a second linear correlation between brine influence and river water at salinities of ~ 30 to 32.

  7. Controls on the Flux, Age, and Composition of Terrestrial Organic Carbon Exported by Rivers to the Ocean

    NASA Astrophysics Data System (ADS)

    Galy, Valier; Peucker-Ehrenbrink, Bernhard; Eglinton, Timothy; Holmes, Robert; Soule, Adam; Goetz, Scott; Laporte, Nadine; Wollheim, Wilfred

    2010-05-01

    Export of organic carbon, alkalinity and silicate-derived Ca and Mg ions to the ocean exerts critical controls on the sequestration of atmospheric carbon. As this export is mediated to a significant extent by river systems, understanding processes that control transport of land-derived matter to the coastal ocean is of fundamental importance to successful models of past and future climates. Scientists from the Woods Hole Oceanographic Institution, the Woods Hole Research Center and the University of New Hampshire have formed a river research consortium that aims at investigating large river systems with a holistic approach. The National Science Foundation is funding this initiative through its Emerging Topics in Biogeochemical Cycles (ETBC) program. Our project focuses on the biogeochemistries of the Lena and Kolyma rivers in the Russian Arctic, the Yangtze river in China, the Ganges and Brahmaputra rivers in India and Bangladesh, the Congo river in central Africa as well as the Fraser river basin in western Canada. Campaign-style sampling using a uniform sampling strategy is complemented by time-series sampling that is accomplished through collaborations with scientists at local institutions such as the East China Normal University in Shanghai (Yangtze), the University of the Fraser Valley in Abbotsford (Fraser), schools and research institutions in eastern Russia (Lena and Kolyma) and the University of Nancy, France (Ganges, Brahmaputra). We combine a standardized sampling approach for organic and inorganic constituents with spatial analyzes of digital, mostly satellite-based data products with the aim of obtaining an integrated understanding of the response of river ecosystems to past, ongoing and future environmental changes. We will present first results with a special emphasis on the age of terrestrial organic carbon exported by the Ganges-Brahmaputra river system.

  8. Increased ocean carbon export in the Sargasso Sea linked to climate variability is countered by its enhanced mesopelagic attenuation

    NASA Astrophysics Data System (ADS)

    Lomas, M. W.; Steinberg, D. K.; Dickey, T.; Carlson, C. A.; Nelson, N. B.; Condon, R. H.; Bates, N. R.

    2010-01-01

    Photosynthetic CO2 uptake by oceanic phytoplankton and subsequent export of particulate organic carbon (POC) to the ocean interior comprises a globally significant biological carbon pump, controlled in part by the composition of the planktonic community. The strength and efficiency of this pump depends upon the balance of particle production in the euphotic zone and remineralization of those particles in the mesopelagic (defined here as depths between 150 and 300 m), but how these processes respond to climate-driven changes in the physical environment is not completely understood. In the Sargasso Sea, from ~1996-2007, we have observed a decade-long >50% increase in euphotic zone integrated autotrophic biomass (estimated from chlorophyll TChl-?), prokaryotic phytoplankton, primary production and shallow (150 m) POC export coinciding with a shift in the mean phase of the winter North Atlantic Oscillation (NAO) from consistently positive to neutral but variable. During this same period mesopelagic POC flux attenuation has doubled such that carbon sequestration below 300 m, the maximum winter/spring ventilation depth, has not changed. The increased mesopelagic POC attenuation appears mediated by changes in plankton community composition and metabolic activity in both the euphotic and mesopelagic zones. These changes are counter to extant hypotheses regarding inter-relationships between phytoplankton community composition, productivity and carbon export, and have significant impacts on how the Sargasso Sea ecosystem, at least, is modeled. Moreover, these time-series observations suggest that processes in the euphotic zone and mesopelagic are tightly coupled and should be considered together in future research.

  9. Freshwater fluxes in the Weddell Gyre: results from ?18O

    PubMed Central

    Brown, Peter J.; Meredith, Michael P.; Jullion, Loc; Naveira Garabato, Alberto; Torres-Valds, Sinhue; Holland, Paul; Leng, Melanie J.; Venables, Hugh

    2014-01-01

    Full-depth measurements of ?18O from 2008 to 2010 enclosing the Weddell Gyre in the Southern Ocean are used to investigate the regional freshwater budget. Using complementary salinity, nutrients and oxygen data, a four-component mass balance was applied to quantify the relative contributions of meteoric water (precipitation/glacial input), sea-ice melt and saline (oceanic) sources. Combination of freshwater fractions with velocity fields derived from a box inverse analysis enabled the estimation of gyre-scale budgets of both freshwater types, with deep water exports found to dominate the budget. Surface net sea-ice melt and meteoric contributions reach 1.8% and 3.2%, respectively, influenced by the summer sampling period, and ?1.7% and +1.7% at depth, indicative of a dominance of sea-ice production over melt and a sizable contribution of shelf waters to deep water mass formation. A net meteoric water export of approximately 37?mSv is determined, commensurate with local estimates of ice sheet outflow and precipitation, and the Weddell Gyre is estimated to be a region of net sea-ice production. These results constitute the first synoptic benchmarking of sea-ice and meteoric exports from the Weddell Gyre, against which future change associated with an accelerating hydrological cycle, ocean climate change and evolving Antarctic glacial mass balance can be determined. PMID:24891394

  10. Freshwater variability in the Arctic: Tracing freshwater sources and quantities from 2005 to 2011 in a transect from Ellesmere Island, Canada to the North Pole

    NASA Astrophysics Data System (ADS)

    Motz, E. A.; Smethie, W. M.

    2011-12-01

    The Switchyard project has gathered data across the Canadian Basin to determine the Arctic Ocean's fractional freshwater composition from three sources: Pacific water, meteoric water (river runoff and precipitation), and sea ice melt water. With a database of the project extending to 2005 as well as using earlier projects' data to date back further, we can view trends and visualize changes in the freshwater content of the Arctic Ocean. In the past decade the Arctic has experienced increases in freshwater with the largest increases from meteoric fractions. In 2008 there was a major increase in meteoric water and decreases in Pacific freshwater fractions. This could be related to the extreme decrease in summer sea ice of 2007. Freshwater inventories across the Canadian Basin vary over the years and show a relationship in the mixed layer of increasing when the Arctic Oscillation (AO) is positive and freshwater is released from the Beaufort Gyre.1 Increases in the quantity of freshwater in the Arctic could lead to greater freshwater exports to the North Atlantic Ocean. This can inhibit the formation of North Atlantic Deep Water and so affect the global thermohaline circulation which moderates much of our planet's climate.2 1 Jones et al. 2008, Pacific freshwater, river water and sea ice meltwater across Arctic Ocean basins: Results from the 2005 Beringia Expedition, Journal of Geophysical Research vol 113, C08012, doi:10.1029/2007JC004124. 32Morison et al. 1998, Hydrography of the upper Arctic Ocean measured from the nuclear submarine U.S.S. Pargo, Deep Sea Research Part I, vol 45, 15-38.

  11. Late Pleistocene ice export events into the Arctic Ocean from the M'Clure Strait Ice Stream, Canadian Arctic Archipelago

    NASA Astrophysics Data System (ADS)

    Stokes, Chris R.; Clark, Chris D.; Darby, Dennis A.; Hodgson, Douglas A.

    2005-12-01

    Rapidly-flowing sectors of an ice sheet (ice streams) can play an important role in abrupt climate change through the delivery of icebergs and meltwater and the subsequent disruption of ocean thermohaline circulation (e.g., the North Atlantic's Heinrich events). Recently, several cores have been raised from the Arctic Ocean which document the existence of massive ice export events during the Late Pleistocene and whose provenance has been linked to source regions in the Canadian Arctic Archipelago. In this paper, satellite imagery is used to map glacial geomorphology in the vicinity of Victoria Island, Banks Island and Prince of Wales Island (Canadian Arctic) in order to reconstruct ice flow patterns in the highly complex glacial landscape. A total of 88 discrete flow-sets are mapped and of these, 13 exhibit the characteristic geomorphology of palaeo-ice streams (i.e., parallel patterns of large, highly elongated mega-scale glacial lineations forming a convergent flow pattern with abrupt lateral margins). Previous studies by other workers and cross-cutting relationships indicate that the majority of these ice streams are relatively young and operated during or immediately prior to deglaciation. Our new mapping, however, documents a large (> 700 km long; 110 km wide) and relatively old ice stream imprint centred in M'Clintock Channel and converging into Viscount Melville Sound. A trough mouth fan located on the continental shelf suggests that it extended along M'Clure Strait and was grounded at the shelf edge. The location of the M'Clure Strait Ice Stream exactly matches the source area of 4 (possibly 5) major ice export events recorded in core PS1230 raised from Fram Strait, the major ice exit for the Arctic Ocean. These ice export events occur at 12.9, 15.6, 22 and 29.8 ka ( 14C yr BP) and we argue that they record vigorous episodes of activity of the M'Clure Strait Ice Stream. The timing of these events is remarkably similar to the North Atlantic's Heinrich events and we take this as evidence that the M'Clure Strait Ice Stream was also activated around the same time. This may hold important implications for the cause of the North Atlantic's Heinrich events and hints at the possibility of a pan-ice sheet response.

  12. Transient Forcing Impacts on the Freshwater Balance in Polar Regions

    NASA Astrophysics Data System (ADS)

    Lehner, Flavio; Raible, Christoph C.; Stocker, Thomas F.; Hofer, Dominik

    2010-05-01

    The hydrological cycle is of fundamental importance for the climate system and increasing attention is being payed to this topic by both observational and model studies. Nevertheless, a comprehensive understanding of the interaction between the hydrological cycle and climate change is still missing -- especially in polar regions. To assess changes of the hydrological cycle in polar regions we use a series of simulations with the Community Climate System Model version 3 (CCSM3) from NCAR. Starting from different initial conditions an ensemble of four transient simulations from 1500 to 2100 (with natural forcing and the SRES scenario A2 from 2000 to 2100) is generated. Thereby future changes are placed in the context of the pre-industrial climate (1500-1870). These long ensemble simulations enable us to assess changes on the basis of a robust data set and to present an extended analysis of the results presented at the 2009 assembly. We found the freshwater cycle and budget in the polar regions to vary little during the pre-industrial period, while the simulations project substantial changes as a response to the increasing greenhouse gas concentrations in the future. These changes in polar regions occur in a temporally and spatially non-uniform way and exert a strong feedback on lower latitudes. In the Arctic region the freshwater import increases stronger than the export, transforming the Arctic Ocean from a freshwater source to a sink with a decreasing density and a rising sea surface height. Discharge from rivers dominates these freshwater budget changes. The Southern Ocean, on the other hand, loses freshwater due to the fact that oceanic export exceeds atmospheric import of freshwater. In the Northern Hemisphere distinct changes of the freshwater discharge through ocean passages to adjacent ocean basins are identified which alter deep-water formation and consequently the Atlantic Meridional Overturning Circulation. The latter is decreasing by about 20% until the end of the 21st century. In the Southern Hemisphere, local modifications in sea ice production and other ocean surface freshwater forcing cause changes in deep-water formation. Based on these projections, substantial changes in the distribution of water masses on hemispheric scale are expected for the 21st and subsequent centuries.

  13. The influence of freshwater and material export on sedimentary facies and benthic processes within the Fly Delta and adjacent Gulf of Papua (Papua New Guinea)

    NASA Astrophysics Data System (ADS)

    Alongi, D. M.; Christoffersen, P.; Tirendi, F.; Robertson, A. I.

    1992-02-01

    Large volumes of freshwater and suspended material debouch from the Fly River in southwestern Papua New Guinea into the Gulf of Papua, greatly influencing the hydrography and sedimentary processes within the river delta and adjacent shelf region. Sedimentary facies within the subtidal regions of the Fly Delta are composed mainly of compacted and eroded very fine black sand, and highly laminated, muddy sand and sandy mud, progressing to prodelta mud with intermixed primary and biogenic structures in the inner Gulf of Papua. These prodelta muds grade further to mixed terrigenous-carbonate deposits southwards into the northern Great Barrier Reef and Torres Strait, and to well-bioturbated, fluid mud northwards into the Gulf of Papua. The transition from physically-dominated, estuarine conditions within the delta to more quiescent, marine conditions on the shelf leads to concomitant changes in sediment chemistry, microbial activity and infaunal and epifaunal communities. Particulate (C, N, P) and dissolved inorganic and organic nutrient concentrations were a function of sediment type (higher in finer deposits) rather than location (delta vs gulf). C: N: P ratios of solid-phase nutrients varied greatly, but were usually less than those predicted by the Redfield ratio. Mean interstitial concentrations of dissolved inorganic nutrients were low (?M range), but dissolved organic carbon, nitrogen and phosphorus levels were equivalent to those found in higher latitude systems. Fluxes of dissolved inorganic nutrients were generally low (?mol m -2 day -1). Flux rates were mostly negative (into the sediment) in the delta suggesting that these deposits are a sink for nutrients. In the offshore deposits, dissolved inorganic fluxes were higher and mostly positive indicating that they are a source for dissolved nutrients. Standing crops of bacteria (range: below detection limits 2.5 10 10 cells g -1 dry wt), meiofauna (range: 5-750 individuals 10 cm -2; 9-1006 ?g dry wt 10 cm -2) and infauna (range: 86-5555 individuals m -2; 0.10-5.85 g AFDW m -2) were generally lower in the delta than in the gulf. The infauna was dominated by nematodes, copepods, foraminifera and small, tube-building, deposit- and suspension-feeding polychaetes and amphipods. Rates of bacterial productivity were very erratic with sediment depth across stations, ranging from 0-2108 mg C m -2 day -1 (DNA synthesis) and from 0-228 mg C m -2 day -1 (protein synthesis), respectively. Rates of benthic respiration and DOC flux across the sediment-water interface were generally high, ranging from 63-780 mg C m -2 day -1 and from -797 to 514 mg C m -2 day -1, respectively. Epibenthos were more diverse (at the phyletic level) at the mid-shelf than inshore, composed mainly of sponges, crabs, crinoids, echinoids, bivalves, hydroids and asteroids. Demersal nekton abundance was low, dominated by the leatherjacket, Paramonacanthus filicauda, the pony fish, Leiognathus splendens and the grunter, Pomadasys argyreus, suggesting limited transfer of infaunal biomass to higher trophic levels. The response of the benthic regime to the export of freshwater and material from the Fly River generally conforms to the RHOADSet al. [(1985) Continental Shelf Research, 4, 189-213] model of benthic response to effluent derived from the Changjiang River in the East China Sea and is similar to infaunal and sedimentary patterns off the Amazon. Nutrient release from the delta sediments contributes little to water-column production, but in the gulf, nutrient efflux from the benthos contributes, on average, 38 and 61% of the annual N and P requirements of phytoplankton production, reflecting closer benthic-pelagic coupling and enrichment of biological productivity in the Gulf of Papua due to nutrient export from the Fly River.

  14. Marinobacter confluentis sp. nov., a lipolytic bacterium isolated from a junction between the ocean and a freshwater lake.

    PubMed

    Park, Sooyeon; Kim, Sona; Kang, Chul-Hyung; Jung, Yong-Taek; Yoon, Jung-Hoon

    2015-12-01

    A Gram-stain-negative, motile, aerobic and rod-shaped bacterium, designated HJM-18T, was isolated from the place where the ocean and a freshwater lake meet at Hwajinpo, South Korea, and subjected to a taxonomic study using a polyphasic approach. Strain HJM-18T grew optimally at 30?C, at pH?7.0-8.0 and in the presence of 1.0-3.0?% (w/v) NaCl. Phylogenetic trees based on 16S rRNA gene sequences showed that strain HJM-18T belonged to the genus Marinobacter. Strain HJM-18T exhibited 16S rRNA gene sequence similarity values of 97.05-98.22?% to the type strains of Marinobacter algicola, Marinobacter flavimaris, Marinobacter adhaerens, Marinobacter salarius, Marinobacter salsuginis, Marinobacter guineae and Marinobacter gudaonensis and of 93.21-96.98?% to the type strains of the other species of the genus Marinobacter. Strain HJM-18T contained Q-9 as the predominant ubiquinone and summed feature 3 (C16?:?1?7c and/or C16?:?1?6c), C16?:?0 and C18?:?1?9c as the major fatty acids. The major polar lipids detected in strain HJM-18T were phosphatidylethanolamine, phosphatidylglycerol and one unidentified aminophospholipid. The DNA G+C content was 58?mol% and the mean DNA-DNA relatedness values with the type strains of the seven phylogenetically related species of the genus Marinobacter were 10-27?%. Differential phenotypic properties, together with phylogenetic and genetic distinctiveness, revealed that strain HJM-18T is separated from recognized species of the genus Marinobacter. On the basis of the data presented, strain HJM-18T represents a novel species of the genus Marinobacter, for which the name Marinobacter confluentis sp. nov. is proposed. The type strain is HJM-18T (?=?KCTC 42705T?=?NBRC 111223T). PMID:26442839

  15. Roseivivax jejudonensis sp. nov., isolated from the junction between the ocean and a freshwater spring at Jeju Island, South Korea.

    PubMed

    Jung, Yong-Taek; Lee, Jung-Sook; Yoon, Jung-Hoon

    2014-11-01

    A Gram-stain negative, coccoid- or oval-shaped and non-gliding bacterial strain, designated CDM-17(T), was isolated from the zone where the ocean and a freshwater spring meet at Jeju island, South Korea, and subjected to a polyphasic taxonomic study. Strain CDM-17(T) was observed to form smooth, circular, glistening, slightly convex, light yellowish pink colonies on marine agar, and was found to grow optimally at pH 7.0-8.0, at 30C and in the presence of 2-3% (w/v) NaCl. A neighbour-joining phylogenetic tree based on 16S rRNA gene sequences showed that strain CDM-17(T) fell within the clade comprising the Roseivivax species, clustering with the type strain of Roseivivax sediminis with which it exhibited 98.3% sequence similarity value. Sequence similarities to the type strains of the other recognized Roseivivax species were 94.7-96.8%. Strain CDM-17(T) was found to contain Q-10 as the predominant ubiquinone and summed feature 8 (C18:1 ?6c and/or C18:1 ?7c) as the major fatty acid. The major polar lipids were identified as phosphatidylcholine, phosphatidylglycerol, an unidentified aminolipid, an unidentified glycolipid and an unidentified lipid. The DNA G+C content of strain CDM-17(T) was determined to be 66.2mol% and its mean DNA-DNA relatedness value with Rsv. sediminis KCTC 23444(T) was 17.52.7%. Differential phenotypic properties, together with the phylogenetic and genetic distinctiveness, revealed that strain CDM-17(T) is distinguishable from recognized Roseivivax species. On the basis of the data presented, strain CDM-17(T) is proposed to represent a novel species of the genus Roseivivax, for which the name Roseivivax jejudonensis sp. nov. is proposed. The type strain is CDM-17(T) (=KCTC 42110(T)=CECT 8625(T)). PMID:25155864

  16. North Atlantic Deep Water export to the Southern Ocean over the past 14 Myr: Evidence from Nd and Pb isotopes in ferromanganese crusts

    USGS Publications Warehouse

    Frank, M.; Whiteley, N.; Kasten, S.; Hein, J.R.; O'Nions, K.

    2002-01-01

    The intensity of North Atlantic Deep Water (NADW) production has been one of the most important parameters controlling the global thermohaline ocean circulation system and climate. Here we present a new approach to reconstruct the overall strength of NADW export from the North Atlantic to the Southern Ocean over the past 14 Myr applying the deep water Nd and Pb isotope composition as recorded by ferromanganese crusts and nodules. We present the first long-term Nd and Pb isotope time series for deep Southern Ocean water masses, which are compared with previously published time series for NADW from the NW Atlantic Ocean. These data suggest a continuous and strong export of NADW, or a precursor of it, into the Southern Ocean between 14 and 3 Ma. An increasing difference in Nd and Pb isotope compositions between the NW Atlantic and the Southern Ocean over the past 3 Myr gives evidence for a progressive overall reduction of NADW export since the onset of Northern Hemisphere glaciation (NHG). The Nd isotope data allow us to assess at least semiquantitatively that the amount of this reduction has been in the range between 14 and 37% depending on location.

  17. Export of newly formed LSW

    NASA Astrophysics Data System (ADS)

    Mller, Katharina; Klein, Birgit; Karstensen, Johannes; Fischer, Jrgen; Baumann, Till; Kanzow, Torsten

    2015-04-01

    The Atlantic meridional overturning circulation represents the strongest mechanism for oceanic northward heat transport. This is accomplished by moving warm water northward in the upper ocean compensated by a deep return flow of cold and dense North Atlantic Deep Water (NADW). Labrador Sea Water (LSW) constitutes the shallowest component of NADW. Since LSW is also supposed to be the most sensitive NADW component to climate change it is of particular interest. LSW is formed by deep convection not only in the centre of the Labrador Sea but also near its western boundary. Recent studies have suggested that LSW formed in the boundary region enters its export route from the Labrador Sea, the Deep Western Boundary Current, faster than LSW originating from the central Labrador Sea. In this study the spatial and temporal evolution of the export of newly formed LSW is investigated. For this purpose hydrographic mooring data from an array located at the western bounndary at 53N starting in the late 1990s until 2014 and data from the Argo float network is used. The averaged seasonal salinity cycle at the array, particularly at the moorings further onshore, shows a pronounced freshwater signal in May indicating the arrival of newly formed LSW in the boundary current. In order to learn more about its preceding pathway and the corresponding export timescale the mooring data is complemented by data from Argo floats. Besides the annual cycles of LSW formation and export, their interannual variations are important aspects affecting the large-scale circulation. For instance, in years of relatively strong convection, as in 2008 and 2012, LSW is observed to pass the boundary current array at 53N earlier, i.e. in February and March, respectively, than in years with weak convection, as in 2007 or 2010. Besides seasonal variations in the boundary current, a possible explanation for the earlier freshwater signal in years of enhanced convection might be a shift in convection sites southwards and/ or towards the boundary.

  18. Flux and age of dissolved organic carbon exported to the Arctic Ocean: A carbon isotopic study of the five largest arctic rivers

    USGS Publications Warehouse

    Raymond, P.A.; McClelland, J.W.; Holmes, R.M.; Zhulidov, A.V.; Mull, K.; Peterson, B.J.; Striegl, R.G.; Aiken, G.R.; Gurtovaya, T.Y.

    2007-01-01

    The export and A ??14C-age of dissolved organic carbon (DOC) was determined for the Yehisey, Lena, Ob', Mackenzie, and Yukon rivers for 2004-2005. Concentrations of DOC elevate significantly with increasing discharge in these rivers, causing approximately 60% of the annual export to occur during a 2-month period following spring ice breakup. We present a total annual flux from the five rivers of ???16 teragrams (Tg), and conservatively estimate that the total input of DOC to the Arctic Ocean is 25-36 Tg, which is ???5-20% greater than previous fluxes. These fluxes are also ???2.5 ?? greater than temperate rivers with similar watershed sizes and water discharge. ??14C-DOC shows a clear relationship with hydrology. A small pool of DOC slightly depleted in ??14C is exported with base flow. The large pool exported with spring thaw is enriched in ??14C with respect to current-day atmospheric ??14C-CO2 values. A simple model predicts that ???50% of DOC exported during the arctic spring thaw is 1-5 years old, ???25% is 6-10 years in age, and 15% is 11-20 years old. The dominant spring melt period, a historically undersampled period export a large amount of young and presumably semilabile DOC to the Arctic Ocean. Copyright 2007 by the American Geophysical Union.

  19. Controls on the Flux, Age, and Composition of Terrestrial Organic Carbon Exported by Rivers to the Ocean

    NASA Astrophysics Data System (ADS)

    Peucker-Ehrenbrink, B.; Eglinton, T. I.; Holmes, R. M.; Galy, V.; Soule, S.; Goetz, S. J.; Laporte, N. T.; Wollheim, W. M.

    2009-12-01

    Export of organic carbon, alkalinity and silicate-derived Ca and Mg ions to the ocean exerts important controls on the sequestration of atmospheric carbon. As this export is mediated to a significant extent by river systems, understanding processes that control transport of land-derived matter to the coastal ocean is of fundamental importance to successful models of past and future climates. Scientists from the Woods Hole Oceanographic Institution, the Woods Hole Research Center and the University of New Hampshire have formed a river research consortium that aims at investigating large river systems with a holistic approach. The National Science Foundation is funding this initiative through its Emerging Topics in Biogeochemical Cycles (ETBC) program. Our project focuses on the biogeochemistries of the Lena and Kolyma rivers in the Russian Arctic, the Yangtze river in China, the Ganges and Brahmaputra rivers in India and Bangladesh, the Congo river in central Africa as well as the Fraser river basin in western Canada. Campaign-style sampling using a uniform sampling strategy is complemented by time-series sampling that is accomplished through collaborations with scientists at local institutions such as the East China Normal University in Shanghai (Yangtze), the University of the Fraser Valley in Abbotsford (Fraser), schools and research institutions in eastern Russia (Lena and Kolyma) and the University of Nancy, France (Ganges, Brahmaputra). We combine a standardized sampling approach for organic and inorganic constituents with spatial analyzes of digital, mostly satellite-based data products with the aim of obtaining an integrated understanding of the response of river ecosystems to past, ongoing and future environmental changes. We will present first results from the Ganges-Brahmaputra, Kolyma as well as the Fraser River systems.

  20. Simulated 21st century's increase in oceanic suboxia by CO2-enhanced biotic carbon export

    NASA Astrophysics Data System (ADS)

    Oschlies, Andreas; Schulz, Kai G.; Riebesell, Ulf; Schmittner, Andreas

    2008-12-01

    The primary impacts of anthropogenic CO2 emissions on marine biogeochemical cycles predicted so far include ocean acidification, global warming induced shifts in biogeographical provinces, and a possible negative feedback on atmospheric CO2 levels by CO2-fertilized biological production. Here we report a new potentially significant impact on the oxygen-minimum zones of the tropical oceans. Using a model of global climate, ocean circulation, and biogeochemical cycling, we extrapolate mesocosm-derived experimental findings of a pCO2-sensitive increase in biotic carbon-to-nitrogen drawdown to the global ocean. For a simulation run from the onset of the industrial revolution until A.D. 2100 under a "business-as-usual" scenario for anthropogenic CO2 emissions, our model predicts a negative feedback on atmospheric CO2 levels, which amounts to 34 Gt C by the end of this century. While this represents a small alteration of the anthropogenic perturbation of the carbon cycle, the model results reveal a dramatic 50% increase in the suboxic water volume by the end of this century in response to the respiration of excess organic carbon formed at higher CO2 levels. This is a significant expansion of the marine "dead zones" with severe implications not only for all higher life forms but also for oxygen-sensitive nutrient recycling and, hence, for oceanic nutrient inventories.

  1. Projected Impact of Climate Change on the Water and Salt Budgets of the Arctic Ocean by a Global Climate Model

    NASA Technical Reports Server (NTRS)

    Miller, James R.; Russell, Gary L.

    1996-01-01

    The annual flux of freshwater into the Arctic Ocean by the atmosphere and rivers is balanced by the export of sea ice and oceanic freshwater. Two 150-year simulations of a global climate model are used to examine how this balance might change if atmospheric greenhouse gases (GHGs) increase. Relative to the control, the last 50-year period of the GHG experiment indicates that the total inflow of water from the atmosphere and rivers increases by 10% primarily due to an increase in river discharge, the annual sea-ice export decreases by about half, the oceanic liquid water export increases, salinity decreases, sea-ice cover decreases, and the total mass and sea-surface height of the Arctic Ocean increase. The closed, compact, and multi-phased nature of the hydrologic cycle in the Arctic Ocean makes it an ideal test of water budgets that could be included in model intercomparisons.

  2. Atmospheric freshwater fluxes and their effect on the global thermohaline circulation

    SciTech Connect

    Zaucker, F.; Stocker, T.F.; Broecker, W.S.

    1994-06-15

    Atmospheric water vapor fluxes were derived from a 1-year data set of horizontal wind speed and specific humidity assimilated from meteorological observations by the European Center for Medium-Range Weather Forecast (ECMWF). Vertically integrated horizontal freshwater fluxes were compared to those of two data sets based on a climatology and on simulations with an atmospheric general circulation model (AGCM). Zonal transports agree fairly well at all latitudes outside the tropics, where fluxes are about double for the AGCM data set. Meridional fluxes of the AGCM and ECMWF data sets show close agreement, while the climatological fluxes are generally smaller with a considerable northward shift in the southern hemisphere. Atmosphere-to-ocean freshwater fluxes were derived from the three data sets. Not only is there substantial disagreement between the data sets, but their zonal averages over the Atlantic, Pacific, and Indian Ocean basins show little resemblance to the respective restoring freshwater fluxes from a 2-dimensional ocean model. If the ocean model is forced with the observed and modeled atmospheric fluxes, we find that the mode of ocean circulation is determined mostly the net flux to the high-latitude oceans and the amount of freshwater exported from the Atlantic basin. The latitudinal structure of the freshwater fluxes in low-latitudes and midlatitudes has little influence on the modeled thermohaline circulation. The fluxes derived from the climatology and ECMWF permit North Atlantic Deep Water (NADW) formation, but a strong freshwater input to the Southern Ocean inhibits Antarctic Bottom Water formation. The AGCM transports so much moisture to the Arctic Ocean that NADW formation is shut down, resulting in a ocean circulation mode of southern sinking in all three ocean basins.

  3. A model-based study of ice and freshwater transport variability along both sides of Greenland

    NASA Astrophysics Data System (ADS)

    Lique, Camille; Treguier, Anne Marie; Scheinert, Markus; Penduff, Thierry

    2009-10-01

    We investigate some aspects of the variability of the Arctic freshwater content during the 1965-2002 period using the DRAKKAR eddy admitting global ocean/sea-ice model (12 km resolution in the Arctic). A comparison with recent mooring sections shows that the model realistically represents the major advective exchanges with the Arctic basin, through Bering, Fram and Davis Straits, and the Barents Sea. This allows the separate contributions of the inflows and outflows across each section to be quantified. In the model, the Arctic freshwater content variability is explained by the sea-ice flux at Fram and the combined variations of ocean freshwater inflow (at Bering) and outflow (at Fram and Davis). At all routes, except trough Fram Strait, the freshwater transport variability is mainly accounted for by the liquid component, with small contributions from the sea-ice flux. The ocean freshwater transport variability through both Davis and Fram is controlled by the variability of the export branch (Baffin Island Current and East Greenland Current, respectively), the variability of the inflow branches playing a minor role. We examine the respective role of velocity and salinity fluctuations in the variability of the ocean freshwater transport. Fram and Davis Straits offer a striking contrast in this regard. Freshwater transport variations across Davis Strait are completely determined by the variations of the total volume flux (0.91 correlation). On the other hand, the freshwater transport through Fram Strait depends both on variations of volume transport and salinity. As a result, there is no significant correlation between the variability of freshwater flux at Fram and Davis, although the volume transports on each side of Greenland are strongly anti-correlated (-0.84). Contrary to Davis Strait, the salinity of water carried by the East Greenland Current through Fram Strait varies strongly due to the ice-ocean flux north of Greenland.

  4. Export fluxes in a naturally fertilized area of the Southern Ocean, the Kerguelen Plateau: ecological vectors of carbon and biogenic silica to depth (Part 2)

    NASA Astrophysics Data System (ADS)

    Rembauville, M.; Blain, S.; Armand, L.; Quéguiner, B.; Salter, I.

    2014-12-01

    The chemical (particulate organic carbon and nitrogen, biogenic silica) and biological (diatoms and faecal pellets) composition of the material exported to a moored sediment trap located under the winter mixed layer of the naturally-fertilized Kerguelen Plateau in the Southern Ocean was studied over an annual cycle. Despite iron availability in spring, the annual particulate organic carbon (POC) export (98.2 mmol m-2) at 289 m was low but annual biogenic silica export was significant (114 mmol m-2). This feature was related to the abundance of empty diatom frustules and the ratio of full : empty cell exerted a first order control in BSi : POC export stoichiometry of biological pump. Chaetoceros Hyalochaete spp. and Thalassiosira antarctica resting spores were found to be responsible for more than 60% of the annual POC that occurred during two very short export events (<14 days in spring-summer) representing the majority of captured export. Low diatom fluxes were observed over the remainder of the year. Faecal pellet contribution to annual carbon flux was low (34%) and reached it's seasonal maximum in autumn and winter (>80%). The seasonal progression of faecal pellet types revealed a clear transition from small spherical shapes (small copepods) in spring, larger cylindrical and ellipsoid shapes in summer (euphausiids and large copepods) and finally large tabular shapes (salps) in autumn and winter. We propose that in this High Biomass, Low Export (HBLE) environment, small, highly silicified, fast-sinking resting spores are able to bypass the high grazing pressure and efficient carbon transfer to higher trophic levels that are responsible for the low fluxes observed the during the remainder of the year. Our study also provides a statistical framework linking the ecological succession of diatom and zooplankton communities to the seasonality of carbon and silicon export within an iron-fertilized bloom region in the Southern Ocean.

  5. An assessment of the Arctic Ocean in a suite of interannual CORE-II simulations. Part I: Sea ice and solid freshwater

    NASA Astrophysics Data System (ADS)

    Wang, Qiang; Ilicak, Mehmet; Gerdes, Rüdiger; Drange, Helge; Aksenov, Yevgeny; Bailey, David A.; Bentsen, Mats; Biastoch, Arne; Bozec, Alexandra; Böning, Claus; Cassou, Christophe; Chassignet, Eric; Coward, Andrew C.; Curry, Beth; Danabasoglu, Gokhan; Danilov, Sergey; Fernandez, Elodie; Fogli, Pier Giuseppe; Fujii, Yosuke; Griffies, Stephen M.; Iovino, Doroteaciro; Jahn, Alexandra; Jung, Thomas; Large, William G.; Lee, Craig; Lique, Camille; Lu, Jianhua; Masina, Simona; Nurser, A. J. George; Rabe, Benjamin; Roth, Christina; Salas y Mélia, David; Samuels, Bonita L.; Spence, Paul; Tsujino, Hiroyuki; Valcke, Sophie; Voldoire, Aurore; Wang, Xuezhu; Yeager, Steve G.

    2016-03-01

    The Arctic Ocean simulated in fourteen global ocean-sea ice models in the framework of the Coordinated Ocean-ice Reference Experiments, phase II (CORE II) is analyzed. The focus is on the Arctic sea ice extent, the solid freshwater (FW) sources and solid freshwater content (FWC). Available observations are used for model evaluation. The variability of sea ice extent and solid FW budget is more consistently reproduced than their mean state in the models. The descending trend of September sea ice extent is well simulated in terms of the model ensemble mean. Models overestimating sea ice thickness tend to underestimate the descending trend of September sea ice extent. The models underestimate the observed sea ice thinning trend by a factor of two. When averaged on decadal time scales, the variation of Arctic solid FWC is contributed by those of both sea ice production and sea ice transport, which are out of phase in time. The solid FWC decreased in the recent decades, caused mainly by the reduction in sea ice thickness. The models did not simulate the acceleration of sea ice thickness decline, leading to an underestimation of solid FWC trend after 2000. The common model behavior, including the tendency to underestimate the trend of sea ice thickness and March sea ice extent, remains to be improved.

  6. Late summer particulate organic carbon export and twilight zone remineralisation in the Atlantic sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Planchon, F.; Cavagna, A.-J.; Cardinal, D.; André, L.; Dehairs, F.

    2013-02-01

    As part of the GEOTRACES Bonus-GoodHope (BGH) expedition (January-March 2008) in the Atlantic sector of the Southern Ocean, particulate organic carbon (POC) export was examined from the surface to the mesopelagic twilight zone using water column distributions of total 234Th and biogenic particulate Ba (Baxs). Surface POC export production was estimated from steady state and non steady state modelling of 234Th fluxes, which were converted into POC fluxes, using the POC/234Th ratio of large, potentially sinking particles (> 53 μm) collected via in situ pumps. Deficits in 234Th activities were observed at all stations from the surface to the bottom of the mixed layer, yielding 234Th export fluxes from the upper 100 m of 496 ± 214 dpm m-2 d-1 to 1195 ± 158 dpm m-2 d-1 for the steady state model and of 149 ±517 dpm m-2 d-1 to 1217 ± 231 dpm m-2 d-1 for the non steady state model. Using the POC/234Thp ratio of sinking particles (ratios varied from 1.7 ± 0.2 μmol dpm-1 to 4.8 ± 1.9 μmol dpm-1) POC export production at 100 m was calculated to range between 0.9 ± 0.4 and 5.1 ± 2.1 mmol C m-2 d-1,assuming steady state and between 0.3 ± 0.9 m-2 d-1 and 4.9 ± 3.3 mmol C m-2 d-1, assuming non steady state. From the comparison of both approaches, it appears that during late summer export decreased by 56 to 16% for the area between the sub-Antarctic zone and the southern Antarctic Circumpolar Current Front (SACCF), whereas it remained rather constant over time in the HNLC area south of the SACCF. POC export represented only 6 to 54% of new production, indicating that export efficiency was, in general, low, except in the vicinity of the SACCF, where export represented 56% of new production. Attenuation of the POC sinking flux in the upper mesopelagic waters (100-600 m depth interval) was evidenced both, from excess 234Th activities and from particulate biogenic Ba (Baxs) accumulation. Excess 234Th activities, reflected by 234Th/238U ratios as large as 1.21 ± 0.05, are attributed to remineralisation/disaggregation of 234Th-bearing particles. The accumulation of excess 234Th in the 100-600 m depth interval ranged from 458 ± 633 dpm m-2 d-1 to 3068 ± 897 dpm m-2 d-1, assuming steady state. Using the POC/234Thp ratio of sinking particles (> 53 μm), this 234Th accumulation flux was converted into a POC remineralisation flux which ranged between 0.9 ± 1.2 mmol C m-2 d-1 and 9.2 ± 2.9 mmol C m-2 d-1. Mesopelagic particulate biogenic Ba has been reported to reflect bacterial degradation of organic matter and to be related to oxygen consumption and bacterial carbon respiration. We observed that the highest Baxs contents (reaching up to > 1000 pM), in general, occurred between 200 and 400 m. Depth-weighted average mesopelagic Baxs (meso-Baxs) values were converted into respired C fluxes, which ranged between 0.23 and 6.4 mmol C m-2 d-1, in good agreement with 234Th-based remineralisation fluxes. A major outcome from this study is the observed significant positive correlation between POC remineralisation as estimated from meso-Baxs contents and from 234Th excess (R2 = 0.73; excluding 2 outliers). Remineralisation of POC in the twilight zone was particularly efficient relative to POC export resulting in negligible bathypelagic (> 600 m) POC export fluxes in the sub-Antarctic zone, the Polar Front zone and the northern Weddell Gyre, while the subtropical zone as well as the vicinity of the SACCF had significant deep POC fluxes.

  7. Deep carbon export from a Southern Ocean iron-fertilized diatom bloom.

    PubMed

    Smetacek, Victor; Klaas, Christine; Strass, Volker H; Assmy, Philipp; Montresor, Marina; Cisewski, Boris; Savoye, Nicolas; Webb, Adrian; d'Ovidio, Francesco; Arrieta, Jess M; Bathmann, Ulrich; Bellerby, Richard; Berg, Gry Mine; Croot, Peter; Gonzalez, Santiago; Henjes, Joachim; Herndl, Gerhard J; Hoffmann, Linn J; Leach, Harry; Losch, Martin; Mills, Matthew M; Neill, Craig; Peeken, Ilka; Rttgers, Rdiger; Sachs, Oliver; Sauter, Eberhard; Schmidt, Maike M; Schwarz, Jill; Terbrggen, Anja; Wolf-Gladrow, Dieter

    2012-07-19

    Fertilization of the ocean by adding iron compounds has induced diatom-dominated phytoplankton blooms accompanied by considerable carbon dioxide drawdown in the ocean surface layer. However, because the fate of bloom biomass could not be adequately resolved in these experiments, the timescales of carbon sequestration from the atmosphere are uncertain. Here we report the results of a five-week experiment carried out in the closed core of a vertically coherent, mesoscale eddy of the Antarctic Circumpolar Current, during which we tracked sinking particles from the surface to the deep-sea floor. A large diatom bloom peaked in the fourth week after fertilization. This was followed by mass mortality of several diatom species that formed rapidly sinking, mucilaginous aggregates of entangled cells and chains. Taken together, multiple lines of evidence-although each with important uncertainties-lead us to conclude that at least half the bloom biomass sank far below a depth of 1,000 metres and that a substantial portion is likely to have reached the sea floor. Thus, iron-fertilized diatom blooms may sequester carbon for timescales of centuries in ocean bottom water and for longer in the sediments. PMID:22810695

  8. Ocean eddies drive the export of salt out of the subtropical gyres: insights from the DRAKKAR 1/12 degree global model

    NASA Astrophysics Data System (ADS)

    Treguier, Anne Marie; Deshayes, Julie; Le Sommer, Julien; Lique, Camille; Madec, Gurvan; Penduff, Thierry; Molines, Jean-Marc; Barnier, Bernard; Bourdalle-Badie, Romain; Talandier, Claude

    2014-05-01

    The spatial distribution of salinity in the ocean results from exchanges with the atmosphere and land (evaporation, precipitation and runoff) as well as transports by the ocean circulation. The eddy contribution to the oceanic meridional transport of salt is quantified for the first time at the global scale in an eddy resolving ocean model at 1/12 degree (DRAKKAR ORCA12 model, based on the NEMO modelling platform). We propose a decomposition of the meridional salt transport which clarifies the link between distribution of salt and freshwater forcing, without defining a "freshwater anomaly" based on an arbitrary reference salinity. The method consists in a decomposition of the meridional transport into i) transport by the time-longitude-depth mean velocity, ii) transport by time-mean velocity recirculations and iii) transport by transient eddy perturbations. The latter is especially large at the northern and southern boundary of the subtropical gyres, where the eddy contribution is comparable in size to the salt transport by the time-mean recirculations. The hierarchy of DRAKKAR simulations demonstrate the sensitivity of eddy transport to the spatial resolution of the model. This eddy transport has to be taken into account when building scenarios for the evolution of ocean salinity in a changing climate.

  9. Projected decreases in future marine export production: the role of the carbon flux through the upper ocean ecosystem

    NASA Astrophysics Data System (ADS)

    Laufkötter, C.; Vogt, M.; Gruber, N.; Aumont, O.; Bopp, L.; Doney, S. C.; Dunne, J. P.; Hauck, J.; John, J. G.; Lima, I. D.; Seferian, R.; Völker, C.

    2015-12-01

    Accurate projections of marine particle export production (EP) are crucial for predicting the response of the marine carbon cycle to climate change, yet models show a wide range in both global EP and their responses to climate change. This is, in part, due to EP being the net result of a series of processes, starting with net primary production (NPP) in the sunlit upper ocean, followed by the formation of particulate organic matter and the subsequent sinking and remineralization of these particles, with each of these processes responding differently to changes in environmental conditions. Here, we compare future projections in EP over the 21st century, generated by four marine ecosystem models under IPCC's high emission scenario RCP8.5, and determine the processes driving these changes. The models simulate small to modest decreases in global EP between -1 and -12 %. Models differ greatly with regard to the drivers causing these changes. Among them, the formation of particles is the most uncertain process with models not agreeing on either magnitude or the direction of change. The removal of the sinking particles by remineralization is simulated to increase in the low and intermediate latitudes in three models, driven by either warming-induced increases in remineralization or slower particle sinking, and show insignificant changes in the remaining model. Changes in ecosystem structure, particularly the relative role of diatoms matters as well, as diatoms produce larger and denser particles that sink faster and are partly protected from remineralization. Also this controlling factor is afflicted with high uncertainties, particularly since the models differ already substantially with regard to both the initial (present-day) distribution of diatoms (between 11-94 % in the Southern Ocean) and the diatom contribution to particle formation (0.6-3.8 times lower/higher than their contribution to biomass). As a consequence, changes in diatom concentration are a strong driver for EP changes in some models but of low significance in others. Observational and experimental constraints on ecosystem structure and how the fixed carbon is routed through the ecosystem to produce export production are urgently needed in order to improve current generation ecosystem models and their ability to project future changes.

  10. Quantifying the Ocean, Freshwater and Human Effects on Year-to-Year Variability of One-Sea-Winter Atlantic Salmon Angled in Multiple Norwegian Rivers

    PubMed Central

    Otero, Jaime; Jensen, Arne J.; L'Abe-Lund, Jan Henning; Stenseth, Nils Chr.; Storvik, Geir O.; Vllestad, Leif Asbjrn

    2011-01-01

    Many Atlantic salmon, Salmo salar, populations are decreasing throughout the species' distributional range probably due to several factors acting in concert. A number of studies have documented the influence of freshwater and ocean conditions, climate variability and human impacts resulting from impoundment and aquaculture. However, most previous research has focused on analyzing single or only a few populations, and quantified isolated effects rather than handling multiple factors in conjunction. By using a multi-river mixed-effects model we estimated the effects of oceanic and river conditions, as well as human impacts, on year-to-year and between-river variability across 60 time series of recreational catch of one-sea-winter salmon (grilse) from Norwegian rivers over 29 years (19792007). Warm coastal temperatures at the time of smolt entrance into the sea and increased water discharge during upstream migration of mature fish were associated with higher rod catches of grilse. When hydropower stations were present in the course of the river systems the strength of the relationship with runoff was reduced. Catches of grilse in the river increased significantly following the reduction of the harvesting of this life-stage at sea. However, an average decreasing temporal trend was still detected and appeared to be stronger in the presence of salmon farms on the migration route of smolts in coastal/fjord areas. These results suggest that both ocean and freshwater conditions in conjunction with various human impacts contribute to shape interannual fluctuations and between-river variability of wild Atlantic salmon in Norwegian rivers. Current global change altering coastal temperature and water flow patterns might have implications for future grilse catches, moreover, positioning of aquaculture facilities as well as the implementation of hydropower schemes or other encroachments should be made with care when implementing management actions and searching for solutions to conserve this species. PMID:21897867

  11. Freshwater pulse experiments in a coupled climate model with bistable AMOC: testing the theory

    NASA Astrophysics Data System (ADS)

    Graham, T.; Jackson, L.; Menary, M.; Palmer, M.

    2012-04-01

    A collapse of the Atlantic meridional overturning circulation (AMOC) could have severe consequences for the climate of Northern Europe and may impact the climate of the whole planet (e.g. Vellinga and Wood, 2002). Several paleoclimate studies have suggested that such events have occurred in the past and may have been responsible for large shifts in Earth's climate. Although such events have been simulated in simple box models and models of intermediate complexity most GCMs have been unable to produce these events. Several recent papers (e.g. Rammstorf, 1999; Pardaens et al., 2003; Drijfhout et al., 2010, Hawkins et al., 2011) have suggested that the direction of freshwater transport by the AMOC at the southern boundary of the Atlantic Ocean (Fov) may be crucial to the stability of the AMOC. Observational estimates suggest that the AMOC exports freshwater from the Atlantic Ocean (Fov < 0) whereas in almost all models without flux adjustments the AMOC imports freshwater (Fov > 0). The latest UK Met Office Hadley Centre climate model (HadGEM3) has a negative Fov as a result of reduced upper ocean salinity biases in the South Atlantic. This suggests that the AMOC may be less stable than in previous models. We will present the first results from a series of freshwater pulse experiments where freshwater is rapidly added to the North Atlantic Ocean to see whether the AMOC will collapse, and furthermore whether it will recover to its initial state.

  12. Downward particle flux and carbon export in the Beaufort Sea, Arctic Ocean; the Malina experiment

    NASA Astrophysics Data System (ADS)

    Miquel, J.-C.; Gasser, B.; Martín, J.; Marec, C.; Babin, M.; Fortier, L.; Forest, A.

    2015-01-01

    As part of the international, multidisciplinary project Malina, downward particle fluxes were investigated by means of a drifting multi-sediment trap mooring deployed at three sites in the Canadian Beaufort Sea in late summer 2009. Mooring deployments lasted for 28-50 h and targeted the shelf-break and the slope along the Beaufort-Mackenzie continental margin, as well as the edge between the Mackenzie Shelf and the Amundsen Gulf. Besides analyses of C and N, the collected material was investigated for pigments, phyto- and microzooplankton, faecal pellets and swimmers. The measured fluxes were relatively low, in the range of 11-54 mg m-2 d-1 for the total mass, 1-15 mg C m-2 d-1 for organic carbon and 0.2-2.5 mg N m-2 d-1 for nitrogen. Comparison with a long-term trap dataset from the same sampling area showed that the short-term measurements were at the lower end of the high variability characterizing a rather high flux regime during the study period. The sinking material consisted of aggregates and particles that were characterized by the presence of hetero- and autotrophic microzooplankters and diatoms and by the corresponding pigment signatures. Faecal pellets contribution to sinking carbon flux was important, especially at depth where they represented up to 25% of the total carbon flux. The vertical distribution of different morphotypes of pellets showed a marked pattern with cylindrical faeces (produced by calanoid copepods) present mainly within the euphotic zone, whereas elliptical pellets (produced mainly by smaller copepods) were more abundant at mesopelagic depths. These features, together with the density of matter within the pellets, highlighted the role of the zooplankton community in the transformation of carbon issued from the primary production and the transition of that carbon from the productive surface zone to the Arctic Ocean's interior. Our data indicate that sinking carbon flux in this late summer period is primarily the result of a heterotrophic driven ecosystem as compared to the system driven by autotrophy earlier in the year.

  13. Downward particle flux and carbon export in the Beaufort Sea, Arctic Ocean; the role of zooplankton

    NASA Astrophysics Data System (ADS)

    Miquel, J.-C.; Gasser, B.; Martín, J.; Marec, C.; Babin, M.; Fortier, L.; Forest, A.

    2015-08-01

    As part of the international, multidisciplinary project Malina, downward particle fluxes were investigated by means of a drifting multi-sediment trap mooring deployed at three sites in the Canadian Beaufort Sea in late summer 2009. Mooring deployments lasted between 28 and 50 h and targeted the shelf-break and the slope along the Beaufort-Mackenzie continental margin, as well as the edge between the Mackenzie Shelf and the Amundsen Gulf. Besides analyses of C and N, the collected material was investigated for pigments, phyto- and microzooplankton, faecal pellets and swimmers. The measured fluxes were relatively low, in the range of 11-54 mg m-2 d-1 for the total mass, 1-15 mg C m-2 d-1 for organic carbon and 0.2-2.5 mg N m-2 d-1 for nitrogen. Comparison with a long-term trap data set from the same sampling area showed that the short-term measurements were at the lower end of the high variability characterizing a rather high flux regime during the study period. The sinking material consisted of aggregates and particles that were characterized by the presence of hetero- and autotrophic microzooplankters and diatoms and by the corresponding pigment signatures. Faecal pellets contribution to sinking carbon flux was important, especially at depths below 100 m, where they represented up to 25 % of the total carbon flux. The vertical distribution of different morphotypes of pellets showed a marked pattern with cylindrical faeces (produced by calanoid copepods) present mainly within the euphotic zone, whereas elliptical pellets (produced mainly by smaller copepods) were more abundant at mesopelagic depths. These features, together with the density of matter within the pellets, highlighted the role of the zooplankton community in the transformation of carbon issued from the primary production and the transition of that carbon from the productive surface zone to the Arctic Ocean's interior. Our data indicate that sinking carbon flux in this late summer period is primarily the result of a heterotrophic-driven ecosystem.

  14. Freshwater fluxes in the Weddell Gyre: results from δ18O.

    PubMed

    Brown, Peter J; Meredith, Michael P; Jullion, Loïc; Naveira Garabato, Alberto; Torres-Valdés, Sinhue; Holland, Paul; Leng, Melanie J; Venables, Hugh

    2014-07-13

    Full-depth measurements of δ(18)O from 2008 to 2010 enclosing the Weddell Gyre in the Southern Ocean are used to investigate the regional freshwater budget. Using complementary salinity, nutrients and oxygen data, a four-component mass balance was applied to quantify the relative contributions of meteoric water (precipitation/glacial input), sea-ice melt and saline (oceanic) sources. Combination of freshwater fractions with velocity fields derived from a box inverse analysis enabled the estimation of gyre-scale budgets of both freshwater types, with deep water exports found to dominate the budget. Surface net sea-ice melt and meteoric contributions reach 1.8% and 3.2%, respectively, influenced by the summer sampling period, and -1.7% and +1.7% at depth, indicative of a dominance of sea-ice production over melt and a sizable contribution of shelf waters to deep water mass formation. A net meteoric water export of approximately 37 mSv is determined, commensurate with local estimates of ice sheet outflow and precipitation, and the Weddell Gyre is estimated to be a region of net sea-ice production. These results constitute the first synoptic benchmarking of sea-ice and meteoric exports from the Weddell Gyre, against which future change associated with an accelerating hydrological cycle, ocean climate change and evolving Antarctic glacial mass balance can be determined. PMID:24891394

  15. POC export from ocean surface waters by means of 234Th/ 238U and 210Po/ 210Pb disequilibria: A review of the use of two radiotracer pairs

    NASA Astrophysics Data System (ADS)

    Verdeny, Elisabet; Masqu, Pere; Garcia-Orellana, Jordi; Hanfland, Claudia; Kirk Cochran, J.; Stewart, Gillian M.

    2009-08-01

    234Th ( T1/2=24.1 d) and 210Po ( T1/2=138.4 d) are particle reactive radioisotopes that are used as tracers for particle cycling in the upper ocean. Particulate organic carbon (POC) export has frequently been estimated using 234Th/ 238U disequilibrium. Recent evidence suggests that 210Po/ 210Pb disequilibrium may be used as an additional tool to examine particle export, given the direct biological uptake of 210Po into cellular material. Differences in these two radioisotope pairs with regard to their half-lives, particle reactivity and scavenging affinity in seawater should provide complementary information to be obtained on the processes occurring in the water column. Here, we review eight different studies that have simultaneously used both approaches to estimate POC export fluxes from the surface ocean. Our aim is to provide a complete "dataset" of all the existing POC flux data derived from the coupled use of both 234Th and 210Po and to evaluate the advantages and limitations of each tracer pair. Our analysis suggests that the simultaneous use of both radiotracers provides more useful comparative data than can be derived from the use of a single tracer alone. The difference in half-lives of 234Th and 210Po enables the study of export production rates over different time scales. In addition, their different biogeochemical behaviour and preferred affinity for specific types of particles leads to the conclusion that 234Th is a better tracer of total mass flux, whereas 210Po tracks POC export more specifically. The synthesis presented here is also intended to provide a basis for planning future sampling strategies and promoting further work in this field to help reveal the more specific application of each tracer under specific water column biogeochemistries.

  16. Appraisal of a molecular approach to infer variations in surface ocean freshwater inputs into the North Atlantic during the last glacial

    NASA Astrophysics Data System (ADS)

    Rosell-Mel, Antoni; Jansen, Eystein; Weinelt, Mara

    2002-11-01

    The thermohaline circulation is considered responsible for regulating climate variability at a global scale [Geochim. Cosmochim. Acta 53 (1989) 2465]. It has been argued that it can be disrupted by changes in surface ocean salinity in the sites of deepwater formation [J. Geophys. Res. 96 (1991) 16811]. However, to date reconstruction of sea surface salinity (SSS) has lacked the accuracy to identify the location, extent and amplitude of past meltwater events [Science 282 (1998) 61]. Recently, a measurement based on alkenones (%37:4) has been shown to be related to types of water masses and perhaps surface salinity in the Nordic Seas [Paleoceanography 13 (1998) 694; Terra Nova 10 (1998) 86]. Here, we present new data from surface sediments that further confirm that it is possible to obtain a linear correlation between %37:4 and salinity. Records of %37:4 from three nearby sediment cores in the NE Atlantic show equivalent profiles, with the highest values occurring in the Heinrich layers (HLs). We propose that downcore %37:4 data can be interpreted in terms of decreases in surface ocean salinity (freshening of surface waters) in response to incoming freshwater from sea-ice and/or icebergs to the core relation. The %37:4 data provides further indication of the locally lower surface ocean salinity that prevailed in the North Atlantic during the last glacial period, and particularly during the Heinrich episodes due to the influx of iceberg meltwater.

  17. Air-sea Heat and Freshwater Fluxes: An Overview of Current Datasets and the Ocean Heat Budget Closure Problem

    NASA Astrophysics Data System (ADS)

    Josey, Simon

    2014-05-01

    Ocean-atmosphere exchanges of heat and water are key elements of the global climate system. Processes controlling these exchanges and their impacts on the ocean will be briefly reviewed with an emphasis on developments in the past decade. The main characteristics of the long term mean exchange fields will also be presented with reference to atmospheric reanalysis, remote sensing and ship observation based datasets. Flux measurement and evaluation techniques will be discussed with reference to observational datasets, particularly the critically important growing network of surface flux buoys. A short review of the many flux datasets that are now available will be given that focuses on the still unsolved ocean heat budget closure problem. Variability in the exchanges will also be considered with a focus on changes associated with large scale modes of atmospheric variability and the effects of anthropogenic climate change. The ocean impacts of changes in the surface fluxes will also be explored in the context of water mass transformation and the ocean overturning circulation. To conclude, the prospects for future improvements to flux datasets through advances in the synthesis of data from different sources and enhanced observational constraints will be discussed.

  18. Climate Change Response of Ocean Net Primary Production (NPP) and Export Production (EP) Regulated by Stratification Increases in The CMIP5 models

    NASA Astrophysics Data System (ADS)

    Fu, W.; Randerson, J. T.; Moore, J. K.

    2014-12-01

    Ocean warming due to rising atmospheric CO2 has increasing impacts on ocean ecosystems by modifying the ecophysiology and distribution of marine organisms, and by altering ocean circulation and stratification. We explore ocean NPP and EP changes at the global scale with simulations performed in the framework of the fifth Coupled Model Inter-comparison Project (CMIP5). Global NPP and EP are reduced considerably by the end of the century for the representative concentration pathway (RCP) 8.5 scenario, although models differ in their significantly in their direct temperature impacts on production and remineralization. The Earth system models used here project similar NPP trends albeit the magnitudes vary substantially. In general, projected changes in the 2090s for NPP range between -2.3 to -16.2% while export production reach -7 to -18% relative to 1990s. This is accompanied by increased stratification by 17-30%. Results indicate that globally reduced NPP is closely related to increased ocean stratification (R2=0.78). This is especially the case for global export production, that seems to be mostly controlled by the increased stratification (R2=0.95). We also identify phytoplankton community impacts on these patterns, that vary across the models. The negative response of NPP to climate change may be through bottom-up control, leading to a reduced capacity of oceans to regulate climate through the biological carbon pump. There are large disagreements among the CMIP5 models in terms of simulated nutrient and oxygen concentrations for the 1990s, and their trends over time with climate change. In addition, potentially important marine biogeochemical feedbacks on the climate system were not well represented in the CMIP5 models, including important feedbacks with aerosol deposition and the marine iron cycle, and feedbacks involving the oxygen minimum zones and the marine nitrogen cycle. Thus, these substantial reductions in primary productivity and export production over the 21st century simulated under the RCP 8.5 scenario were likely conservative estimates, and may need to be revised as marine biogeochemistry in Earth System Models (ESMs) continues to be developed.

  19. Recognition of extensive freshwater and brackish marshes and of multiple transgressions and regressions: The Holocene wetlands of the Delaware Bay and Atlantic Ocean coasts

    SciTech Connect

    Yi, H.I. . Dept. of Geology)

    1992-01-01

    Extensive and closely spaced cores (204) were analyzed to find detailed facies (microfacies) and paleoenvironments in the subsurface sediments along the Delaware Bay and Atlantic Ocean. To determine detailed facies and paleoenvironments, several composite methods were employed: traditional lithological analysis, botanical identification, macro- and micro-paleontological analysis, grain size analysis, organic and inorganic content, water content, mineral composition, particulate plant, and C-14 dating. Twenty-two sedimentary microfacies were identified in the surface and subsurface sediments of the study area. Most of the lower section of the Holocene sediments contained freshwater and brackish marsh microfacies which alternated or intercalated with fluvial microfacies or brackish tidal flat/tidal stream microfacies. After tides encroached upon the freshwater marshes and swamps, several events of transgression and regression were recorded in the stratigraphic section. Finally, saline paleoenvironments predominated at the top section of subsurface sediments. Within saline facies, three subgroups of salt marsh microfacies were identified: high salt marsh sub-microfacies, middle salt marsh sub-microfacies were identified: high salt marsh sub-microfacies, middle salt marsh sub-microfacies, and low salt marsh sub-microfacies. The major controlling factors of these paleoenvironmental changes were local relative sea-level fluctuations, sediment supply, pre-Holocene configuration, fluvial activity, groundwater influence, climatic change, sediment compaction, tectonics, isostasy and biological competition. Ten events of transgression and regression in some areas were found in about 2,000 years, but other areas apparently contained no evidence of multiple events of transgression and regression. Some other areas showed one or two distinctive events of transgression and regression. Therefore, further investigation is necessary to understand the details of these records.

  20. Interannual variations of Dense Shelf Water in the Sea of Okhotsk affected by oceanic freshwater transport in the North Pacific subpolar gyre

    NASA Astrophysics Data System (ADS)

    Uehara, H.; Kruts, A. A.; Mitsudera, H.; Nakamura, T.; Volkov, Y. N.; Wakatsuchi, M.

    2012-12-01

    We use a new hydrographic dataset to investigate the effect of oceanic freshwater (salt) transport on the interannual variations of Dense Shelf Water (DSW) formation in the Sea of Okhotsk. DSW is formed by brine rejection due to sea-ice production in the northern shelf of the Sea of Okhotsk and is transported to the intermediate layer after its formation. DSW is one of the source waters of the North Pacific Intermediate Water so that it contributes to the North Pacific ventilation and plays a role in the global thermohaline circulation. DSW formation and advection also leads to the transport of the materials such as carbon and iron. The Sea of Okhotsk is notorious for its poor availability of the observation data. The new dataset contains the Russian hydrographic observations in the Sea of Okhotsk and Bering Sea, which enables us to study the DSW variations and their causes. The time series of DSW salinity and potential density show that they have the decreasing trends since 1950 as well as the significant interannual variations. The trends are consistent with observed decreasing of sea-ice extent due to air-temperature rise over Siberia. We suggest that the advection of salinity anomalies (freshwater transport) from the Bering Sea changes the surface layer salinity in the northern shelf of the Sea of Okhotsk and preconditions the DSW variations. Formation mechanisms for the salinity anomalies in the Bering Sea are also discussed. These results suggest that we need to improve the salinity distributions reproduced in numerical models to predict the changes in the ventilation and overturning in the North Pacific under the influence of the strengthened hydrological cycle in future.

  1. Shallow-depth CaCO3 dissolution: Evidence from excess calcium in the South China Sea and its export to the Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Cao, Zhimian; Dai, Minhan

    2011-06-01

    Variations in seawater-dissolved calcium ion (Ca2+) are small but substantial, which provides information essential to establish the oceanic calcium carbonate (CaCO3) dissolution flux. In this study, high-precision data of Ca2+ were collected in the South China Sea (SCS), the largest marginal sea of the western North Pacific, and its precursor, the West Philippine Sea (WPS), on the basis of two cruises conducted in 2007 and in 2008. An excess Ca2+ of 13 5 ?mol kg-1 was observed in the SCS subsurface water at 200-800 m relative to the WPS, and we suggest that such an excess is attributed to in situ CaCO3 dissolution at a rate of 0.5 mmol m-2 d-1 in the SCS shallow subsurface water. Through subsurface water outflow, this shallow-depth CaCO3 dissolution may provide a Ca2+ export flux of (0.8 0.3) 1012 mol yr-1 from the SCS to the WPS, establishing it as an important Ca2+ source from the SCS to the interior Pacific Ocean. This study indicates, for the first time, that along with the benthic processes, CaCO3 dissolution in waters at shallow depth in marginal seas could also contribute to Ca2+ and total alkalinity accumulations in the upper layer of the open ocean, which would ultimately enhance the buffer capacity of the world ocean in the context of rising anthropogenic CO2.

  2. Freshwater Macroinvertebrates.

    ERIC Educational Resources Information Center

    Nalepa, T. F.

    1978-01-01

    Presents a literature review of freshwater biology particularly freshwater macroinvertebrates and their effect on water pollution, covering publications of 1976-77. A list of 158 references is also presented. (HM)

  3. Human freshwater demand for economic activity and ecosystems in Taiwan.

    PubMed

    Ferng, Jiun-Jiun

    2007-12-01

    Freshwater is necessary to economic activity, and humans depend on goods and services generated by water-dependent ecosystems. However, national freshwater management usually focuses on direct use of domestic freshwater. With an increasing scarcity of freshwater, attention has turned to two indirect uses of freshwater by humans. The first indirect use is freshwater used by foreign countries when producing products for export. The second use is freshwater required by local ecosystems: human survival and development depend on goods and services generated in these ecosystems. This work adopted Taiwan as a case study. In addition to two widely recognized ecosystem freshwater demands, evapotranspiration and reversed river flow, this study suggests that freshwater is a constituent of some abiotic components, such as groundwater in aquifers, because excessive withdrawal has already caused significant land subsidence in Taiwan. Moreover, the estimated results show that Taiwan's net imports of freshwater through trade amounts to approximately 25% of its total freshwater use for economic production. Integrating industrial policy, trade policy, and national freshwater management is a useful approach for developing strategies to limit the growing use of freshwater in Taiwan. Policy implications are then developed by further analyzing withdrawal sources of freshwater (domestic and foreign) for supporting economic production in Taiwan and identifying the factors (domestic final demand and export) driving freshwater-intensive products. PMID:17899249

  4. Millennial-Scale Variations of Nitrogen Isotopes and Export Proxies in the Subarctic Pacific During MIS 3: Evidence for an Oceanic Fertility Switch?

    NASA Astrophysics Data System (ADS)

    Galbraith, E. D.; Schmittner, A.; Pedersen, T. F.

    2005-12-01

    Millennial-scale variability has previously been observed in both the nitrogen isotopic ratio (?15N) and paleoproductivity proxies in sediments of the Arabian Sea and the Californian margin. Here we show that hemipelagic sediments from a seamount in the Gulf of Alaska (ODP site 887) record similar millennial variability in ?15N and biogenic components during Marine Isotope Stage 3, with a tantalizing resemblance to North Atlantic temperature records. The subarctic Pacific record can be interpreted in several ways. One possibility is that periods of intense aridity promoted enhanced dust transport to the North Pacific, alleviating Fe limitation and allowing more complete utilization of the available nitrate. Although the age constraints are insufficient to distinguish stadials from interstadials, one would expect stadial periods to be more arid and, hence, to be correlated with high ?15N and productivity. However, in this case the Gulf of Alaska ?15N record would be antiphased with ?15N records of the Oregon and California margins, which seems unlikely. Alternatively, Fe could have been delivered by enhanced offshore transport of shelf material during periods of sea level rise, resulting in a positive phasing between the Gulf of Alaska and other ?15N records, but without providing a mechanistic link between them. A more parsimonious explanation is that nitrogen isotopes and export productivity varied in phase, on millennial timescales, at all of these locations. We propose that this resulted from millennial changes in the distribution of nutrients and oxygen in the ocean, caused by changes in the physical circulation. During interstadials, strong NADW formation maintained relatively low deep water nutrient concentrations, ensuring a rich supply of nutrients in the upper ocean. The cessation of NADW formation during stadials allowed the migration of nutrients to the deep sea, stripping the upper ocean of its potential fertility. The marine nitrogen cycle responded to these events through the modulation of thermocline suboxia by upper ocean fertility. During interstadials when the upper ocean was relatively nutrient-rich, expanded thermocline suboxia drove accelerated denitrification, producing an increase in ?15N near denitrification zones. When the upper ocean became nutrient-poor during stadials, thermocline suboxia contracted and ?15N fell to lower values. Enhanced ventilation in much of the upper ocean, particularly in the North Pacific, may have further increased the subsurface oxygen supply during stadials. If valid, this mechanism would have had some effect on atmospheric trace gases including carbon dioxide and nitrous oxide.

  5. Preferential remineralization of dissolved organic phosphorus and non-Redfield DOM dynamics in the global ocean: Impacts on marine productivity, nitrogen fixation, and carbon export

    NASA Astrophysics Data System (ADS)

    Letscher, Robert T.; Moore, J. Keith

    2015-03-01

    Selective removal of nitrogen (N) and phosphorus (P) from the marine dissolved organic matter (DOM) pool has been reported in several regional studies. Because DOM is an important advective/mixing pathway of carbon (C) export from the ocean surface layer and its non-Redfieldian stoichiometry would affect estimates of marine export production per unit N and P, we investigated the stoichiometry of marine DOM and its remineralization globally using a compiled DOM data set. Marine DOM is enriched in C and N compared to Redfield stoichiometry, averaging 317:39:1 and 810:48:1 for C:N:P within the degradable and total bulk pools, respectively. Dissolved organic phosphorus (DOP) is found to be preferentially remineralized about twice as rapidly with respect to the enriched C:N stoichiometry of marine DOM. Biogeochemical simulations with the Biogeochemical Elemental Cycling model using Redfield and variable DOM stoichiometry corroborate the need for non-Redfield dynamics to match the observed DOM stoichiometry. From our model simulations, preferential DOP remineralization is found to increase the strength of the biological pump by ~9% versus the case of Redfield DOM cycling. Global net primary productivity increases ~10% including an increase in marine nitrogen fixation of ~26% when preferential DOP remineralization and direct utilization of DOP by phytoplankton are included. The largest increases in marine nitrogen fixation, net primary productivity, and carbon export are observed within the western subtropical gyres, suggesting the lateral transfer of P in the form of DOP from the productive eastern and poleward gyre margins may be important for sustaining these processes downstream in the subtropical gyres.

  6. Deterioration of perennial sea ice in the Beaufort Gyre from 2003 to 2012 and its impact on the oceanic freshwater cycle

    NASA Astrophysics Data System (ADS)

    Krishfield, R. A.; Proshutinsky, A. Y.; Tateyama, K.; Williams, W. J.; Carmack, E. C.; McLaughlin, F. A.; Timmermans, M. L. E.

    2014-12-01

    Time series of ice draft from 2003-2012 from moored sonar data are used to investigate variability and describe the reduction of the perennial sea ice cover in the Beaufort Gyre (BG), culminating in the extreme minimum in 2012. Negative trends in median ice drafts and most ice fractions are observed, while open water and thinnest ice fractions (<0.3 m) have increased, attesting to the ablation or removal of the older sea-ice from the BG over the nine year period. Monthly anomalies indicate a shift occurred toward thinner ice after 2007, in which the thicker ice evident at the northern stations was reduced. Differences in the ice characteristics between all of the stations also diminished, so that the ice cover throughout the region became statistically homogenous. The moored data are used to calibrate ice thickness estimates from satellite radiometer data to estimate ice volume changes throughout the BG. Summer solid fresh water content decreased drastically in consecutive years from 730 km3 in 2006 to 570 km3 in 2007, and to 240 km3 in 2008. After a short rebound, solid fresh water fell below 220 km3 in 2012. Meanwhile hydrographic data indicate that liquid fresh water in the BG in summer increased 5410 km3 from 2003 to 2010 and decreased at least 210 km3 by 2012. The reduction of both solid and liquid fresh water components indicates a net export of 320 km3 of fresh water from the region occurred between 2010 and 2012, suggesting that the ocean anticyclonic circulation regime has weakened.

  7. An approach to estimate the freshwater contribution from glacial melt and precipitation in East Greenland shelf waters using colored dissolved organic matter (CDOM)

    NASA Astrophysics Data System (ADS)

    Stedmon, Colin A.; Granskog, Mats A.; Dodd, Paul A.

    2015-02-01

    Changes in the supply and storage of freshwater in the Arctic Ocean and its subsequent export to the North Atlantic can potentially influence ocean circulation and climate. In order to understand how the Arctic freshwater budget is changing and the potential impacts, it is important to develop and refine empirical approaches for tracing freshwater contributions. This in turn can help develop and validate model simulations. Arctic rivers are an important source of freshwater and stable oxygen isotope measurements are used to separate contributions from meteoric water (river, glacial, and precipitation) and sea ice melt. We develop this approach further and investigate the use of an additional tracer, colored dissolved organic matter (CDOM), which is largely specific to freshwater originating from Arctic rivers. A robust relationship between the freshwater contribution from meteoric water and CDOM is derived from 4 years of measurements in Fram Strait (2009-2012), combined with measurements from the East Greenland shelf and Dijmpha Sound (NE Greenland). Results confirm a high contribution of riverine CDOM in Arctic halocline waters with salinities >31.5 and indicate the importance of shelf processes (riverine input and sea ice formation), while previously, these waters where thought to be derived from open sea processes (cooling and sea ice formation) in the northern Barents and Kara Seas. In Greenlandic coastal waters the meteoric water contribution is influenced by Greenland ice sheet meltwater and deviations from the CDOM-meteoric water relationships found are applied to quantify meltwater contribution along the East Greenland shelf waters (0-13%).

  8. Simiduia curdlanivorans sp. nov., a curdlan-degrading bacterium isolated from the junction between the ocean and a freshwater spring, and emended description of the genus Simiduia.

    PubMed

    Park, Sooyeon; Kim, Soo-In; Jung, Yong-Taek; Yoon, Jung-Hoon

    2014-11-01

    A Gram-stain-negative, aerobic, non-spore-forming, non-flagellated and rod-shaped bacterial strain, designated DMCK3-4(T), was isolated from the zone where the ocean and a freshwater spring meet at Jeju island, South Korea. Strain DMCK3-4(T) grew optimally at 30 C, at pH 7.0-8.0 and in the presence of 2.0% (w/v) NaCl. Phylogenetic trees based on 16S rRNA gene sequences revealed that strain DMCK3-4(T) clustered with the strains of three members of the genus Simiduia, with which it exhibited 97.0-99.0% sequence similarity. Sequence similarities to the type strains of the other species with validly published names were less than 92.2%. Strain DMCK3-4(T) contained Q-8 as the predominant ubiquinone and summed feature 3 (C(16:1)?7c and/or C(16:1)?6c), C(17:1)?8c, C(16:0), C(17:0) and C(18:1)?7c as the major fatty acids. The major polar lipids of strain DMCK3-4(T) were phosphatidylethanolamine, phosphatidylglycerol, two unidentified glycolipids, one unidentified lipid and one unidentified aminolipid. The DNA G+C content of strain DMCK3-4(T) was 51.8 mol% and its mean DNA-DNA relatedness values with Simiduia agarivorans KCTC 23176(T), Simiduia areninigrae KCTC 23293(T) and Simiduia litorea NRIC 0917(T) were 23-34%, respectively. The differential phenotypic properties, together with the phylogenetic and genetic distinctiveness, revealed that strain DMCK3-4(T) is distinct from other species of the genus Simiduia. On the basis of the data presented, strain DMCK3-4(T) is considered to represent a novel species of the genus Simiduia, for which the name Simiduia curdlanivorans sp. nov. is proposed. The type strain is DMCK3-4(T) (?=?KCTC 42075(T)?=CECT 8570(T)). An emended description of the genus Simiduia is also proposed. PMID:25106923

  9. Modeling responses of diatom productivity and biogenic silica export to iron enrichment in the equatorial Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Chai, F.; Jiang, M.-S.; Chao, Y.; Dugdale, R. C.; Chavez, F.; Barber, R. T.

    2007-09-01

    Using a three-dimensional physical-biogeochemical model, we have investigated the modeled responses of diatom productivity and biogenic silica export to iron enrichment in the equatorial Pacific, and compared the model simulation with in situ (IronEx II) iron fertilization results. In the eastern equatorial Pacific, an area of 540,000 km2 was enhanced with iron by changing the photosynthetic efficiency and silicate and nitrogen uptake kinetics of phytoplankton in the model for a period of 20 days. The vertically integrated Chl a and primary production increased by about threefold 5 days after the start of the experiment, similar to that observed in the IronEx II experiment. Diatoms contribute to the initial increase of the total phytoplankton biomass, but decrease sharply after 10 days because of mesozooplankton grazing. The modeled surface nutrients (silicate and nitrate) and TCO2 anomaly fields, obtained from the difference between the "iron addition" and "ambient" (without iron) concentrations, also agreed well with the IronEx II observations. The enriched patch is tracked with an inert tracer similar to the SF6 used in the IronEx II. The modeled depth-time distribution of sinking biogenic silica (BSi) indicates that it would take more than 30 days after iron injection to detect any significant BSi export out of the euphotic zone. Sensitivity studies were performed to establish the importance of fertilized patch size, duration of fertilization, and the role of mesozooplankton grazing. A larger size of the iron patch tends to produce a broader extent and longer-lasting phytoplankton blooms. Longer duration prolongs phytoplankton growth, but higher zooplankton grazing pressure prevents significant phytoplankton biomass accumulation. With the same treatment of iron fertilization in the model, lowering mesozooplankton grazing rate generates much stronger diatom bloom, but it is terminated by Si(OH)4 limitation after the initial rapid increase. Increasing mesozooplankton grazing rate, the diatom increase due to iron addition stays at minimum level, but small phytoplankton tend to increase. The numerical model experiments demonstrate the value of ecosystem modeling for evaluating the detailed interaction between biogeochemical cycle and iron fertilization in the equatorial Pacific.

  10. Deep and bottom water export from the Southern Ocean to the Pacific over the past 38 million years

    USGS Publications Warehouse

    van de Flierdt, T.; Frank, M.; Halliday, A.N.; Hein, J.R.; Hattendorf, B.; Gunther, D.; Kubik, P.W.

    2004-01-01

    The application of radiogenic isotopes to the study of Cenozoic circulation patterns in the South Pacific Ocean has been hampered by the fact that records from only equatorial Pacific deep water have been available. We present new Pb and Nd isotope time series for two ferromanganese crusts that grew from equatorial Pacific bottom water (D137-01, "Nova," 7219 m water depth) and southwest Pacific deep water (63KD, "Tasman," 1700 m water depth). The crusts were dated using 10Be/9Be ratios combined with constant Co-flux dating and yield time series for the past 38 and 23 Myr, respectively. The surface Nd and Pb isotope distributions are consistent with the present-day circulation pattern, and therefore the new records are considered suitable to reconstruct Eocene through Miocene paleoceanography for the South Pacific. The isotope time series of crusts Nova and Tasman suggest that equatorial Pacific deep water and waters from the Southern Ocean supplied the dissolved trace metals to both sites over the past 38 Myr. Changes in the isotopic composition of crust Nova are interpreted to reflect development of the Antarctic Circumpolar Current and changes in Pacific deep water circulation caused by the build up of the East Antarctic Ice Sheet. The Nd isotopic composition of the shallower water site in the southwest Pacific appears to have been more sensitive to circulation changes resulting from closure of the Indonesian seaway. Copyright 2004 by the American Geophysical Union.

  11. Seasonality and long term trends in dissolved carbon export from large rivers to the Arctic Ocean, and potential effects on coastal ocean acidification (Invited)

    NASA Astrophysics Data System (ADS)

    Tank, S. E.; Kokelj, S. V.; Raymond, P. A.; Striegl, R. G.; McClelland, J. W.; Holmes, R. M.; Spencer, R. G.

    2013-12-01

    Large Arctic rivers show marked seasonality in constituent flux as a result of variations in flowpath throughout the yearly cycle. Here, we use measurements collected from the mouths of the six largest rivers draining to the Arctic Ocean to explore seasonal variation in dissolved inorganic and dissolved organic carbon (DIC, DOC) flux, and the effect of this flux on nearshore ocean processes. This work uses data from the Yukon and Mackenzie Rivers in North America, and the Kolyma, Lena, Yenisey, and Ob' in Siberia. Mean monthly concentrations of riverine DIC vary synchronously across all rivers, peaking under ice and reaching a low point immediately after the spring freshet. Monthly climatologies for DIC, in addition to similarly constructed climatologies for Ca2+, show that the input of riverwater universally causes aragonite to be undersaturated in riverine-influenced nearshore regions, with an effect that is greater for the Siberian coast than for western North America, and greater in the spring-winter than in the late summer and fall. Because seasonal trends and geographic variation in DOC concentration are opposite to that for DIC in these large rivers, degradation of DOC to CO2 in the nearshore Arctic should accentuate seasonal and spatial patterns in aragonite undersaturation in Arctic coastal regions. Datasets that extend DIC and DOC concentration measurements back to the early 1970's (DIC) and early 1980's (DOC) near the mouth of the Mackenzie River in the western Canadian Arctic indicate that the summertime concentration and flux of these constituents has been increasing over time in this region. While evidence from other regions of the pan-Arctic, and data gathered from smaller sub-catchment studies indicate that this trend is not universal for DOC, there is growing evidence for a consistent increase in summertime DIC flux across both time and gradients of decreasing permafrost extent. These changes, in turn, could have broad implications for both nearshore processes and the larger Arctic carbon cycle. Understanding how riverine dissolved carbon flux is changing in northern regions as a result of variations in hydrologic seasonality and flowpath will greatly aid our understanding of global change across broad spatial scales in the north.

  12. Export fluxes in a naturally fertilized area of the Southern Ocean, the Kerguelen Plateau: seasonal dynamic reveals long lags and strong attenuation of particulate organic carbon flux (Part 1)

    NASA Astrophysics Data System (ADS)

    Rembauville, M.; Salter, I.; Leblond, N.; Gueneugues, A.; Blain, S.

    2014-12-01

    A sediment trap moored in the naturally iron-fertilized Kerguelen plateau in the Southern Ocean provided an annual record of particulate organic carbon and nitrogen fluxes at 289 m. At the trap deployment depth current speeds were low (∼10 cm s-1) and primarily tidal-driven (M2 tidal component) providing favorable hydrodynamic conditions for the collection of flux. Particulate organic carbon (POC) flux was generally low (<0.5 mmol m-2 d-1) although two episodic export events (<14 days) of 1.5 mmol m-2 d-1 were recorded. These increases in flux occurred with a 1 month time lag from peaks in surface chlorophyll and together accounted for approximately 40% of the annual flux budget. The annual POC flux of 98.2 4.4 mmol m-2 yr-1 was relatively low considering the shallow deployment depth, but similar to deep-ocean (>2 km) fluxes measured from similarly productive iron-fertilized blooms. Comparison of the sediment trap data with complementary estimates of biomass accumulation and export indicate that ∼90% of the flux was lost between 200 and 300 m. We hypothesize that grazing pressure, including mesozooplankton and mesopelagic fishes, may be responsible for rapid flux attenuation and the High Biomass Low Export regime characterizing the Kerguelen bloom. The importance of plankton community structure in controlling the temporal variability of export fluxes is addressed in a companion paper.

  13. Particulate organic carbon export fluxes on Chukchi Shelf, western Arctic Ocean, derived from 210Po/210Pb disequilibrium

    NASA Astrophysics Data System (ADS)

    He, Jianhua; Yu, Wen; Lin, Wuhui; Men, Wu; Chen, Liqi

    2015-05-01

    Fluxes of particulate organic carbon (POC) were derived from 210Po/210Pb disequilibrium during the 4th Chinese National Arctic Research Expedition (CHINARE-4) from July 1 to September 28, 2010. Average residence times of particulate 210Po in the euphotic zone were -16.00 a to 1.54 a, which are higher than those of dissolved 210Po (-6.89 a to -0.70 a). Great excesses of dissolved 210Po were observed at all stations, with an average 210Po/210Pb ratio of 1.91±0.20, resulting from 210Pb atmospheric deposition after sea ice melt. POC fluxes from the euphotic zone were estimated by two methods (E and B) in the irreversible scavenging model. Estimated POC fluxes were 945-126 mmol C/(m2·a) and 1 848-109 mmol C/(m2·a) by methods E and B, respectively, both decreasing from low to high latitude. The results are comparable to previous works for the same region, indicating efficient biological pumping in the Chukchi Sea. The results can improve understanding of the carbon cycle in the western Arctic Ocean.

  14. Upper ocean response of the Mesoamerican Barrier Reef System to Hurricane Mitch and coastal freshwater inputs: A study using Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color data and a nested-grid ocean circulation model

    NASA Astrophysics Data System (ADS)

    Sheng, Jinyu; Wang, Liang; AndrFouT, Serge; Hu, Chuanmin; Hatcher, Bruce G.; Muller-Karger, Frank E.; Kjerfve, BjRn; Heyman, William D.; Yang, Bo

    2007-07-01

    The passage of category-5 Hurricane Mitch through the Mesoamerican Barrier Reef System (MBRS) in October 1998 was an extreme event with the potential to create unusual patterns of reef connectivity. The impact of this hurricane on the upper ocean of the MBRS is investigated using a triply nested grid ocean circulation modeling system. The model results are validated with contemporaneous ocean color data from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) satellite and oceanographic measurements in the MBRS. The nested grid system is forced by 6-hourly National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) winds for the first 294 days prior to the arrival of the hurricane in the MBRS, and then by the combination of the NCEP/NCAR wind-forcing and an idealized vortex representative of Mitch for the following 20 days. The system is also forced by the monthly mean sea surface heat and freshwater fluxes and buoyancy forcing associated with major river discharges and storm-induced precipitation in the western Caribbean Sea. The simulated upper ocean circulation during Mitch is characterized by strong and divergent currents under the storm and intense near-inertial currents and sea surface temperature cooling behind the storm. The nested grid system also reproduces the buoyant estuarine plumes extending from the coast off Honduras as inferred from SeaWiFS satellite data and detected in field measurements at Gladden Spit in Belize shortly after the passage of Hurricane Mitch. The present model results suggest that populations of site-attached organisms associated with nearshore and offshore reef features that are dynamically isolated in normal conditions experienced greater potential for ecological connection under Mitch's extreme conditions.

  15. The stabilizing effect of sea-ice on a freshwater perturbation

    NASA Astrophysics Data System (ADS)

    Jensen, Mari F.; Nisancioglu, Kerim H.; Nilsson, Johan

    2015-04-01

    A retreating sea-ice cover is one of the hypothesized mechanisms for the abrupt warming observed during Dansgaard-Oeschger events of the last glacial. It has been proposed that a warming of the subsurface ocean during cold stadials could explain the rapid retreating sea-ice cover in the Nordic Seas at the start of each interstadial (Dokken et al., 2013). The warming of the subsurface ocean would gradually weaken the vertical stratification and lead to a sudden convective overturning as the vertical density difference disappeared. In this study, we show that the circulation can become unstable even before the vertical density difference vanishes. We study the stability of a salinity-dominated circulation to freshwater perturbations in the presence of sea-ice, by using a one-dimensional, analytical model. The model represents the sea-ice covered Nordic Seas, and consists of a sea-ice component and a two-layer ocean; a cold, fresh surface layer above a warm, salty deep ocean. The sea-ice thickness depends on the atmospheric energy fluxes as well as the ocean heat flux, and we impose a thickness-dependent sea-ice export. The stabilizing effect of sea-ice to a freshwater perturbation is shown to depend on the representation of vertical mixing. In a system where the mixing increases with density differences, the sea-ice acts as a positive feedback to a freshwater perturbation. If the mixing decreases with density differences, the sea-ice acts as a negative feedback. However, both representations lead to a circulation that breaks down when the freshwater input at the surface is small. As a consequence, we get rapid changes in sea-ice. In addition to low freshwater values, increasing deep-ocean temperatures promote instability and the disappearance of sea-ice. Dokken, T. M., Nisancioglu, K. H., Li, C., Battisti, D. S. and Kissel, C. (2013), `Dansgaard Oeschger cycles: interactions between ocean and sea ice intrinsic to the Nordic Seas', Paleoceanography 28

  16. Freshwater Wetlands.

    ERIC Educational Resources Information Center

    Naturescope, 1986

    1986-01-01

    Provides descriptions about freshwater wetlands, such as marshes, swamps, and bogs. Contains three learning activities which deal with unusual wetland plants, the animals and plants in a typical marsh, and the effects of a draught on a swamp. Included are reproducible handouts and worksheets for two of the activities. (TW)

  17. Primary production and carbon export rates across the subpolar N. Atlantic Ocean basin based on triple oxygen isotope and dissolved O2 and Ar gas measurements

    NASA Astrophysics Data System (ADS)

    Quay, P.; Stutsman, J.; Steinhoff, T.

    2012-06-01

    Gross photosynthetic O2 production (GOP) rates in the subpolar North Atlantic Ocean were estimated using the measured isotopic composition of dissolved oxygen in the surface layer on samples collected on nine transits of a container ship between Great Britain and Canada during March 2007 to June 2008. The mean basin-wide GOP rate of 226 48 mmol O2 m-2 d-1 during summer was double the winter rate of 107 41 mmol O2 m-2 d-1. Converting these GOP rates to equivalent 14C-based PP (14C-PPeqv) yielded rates of 1005 216 and 476 183 mg C m-2 d-1 in summer and winter, respectively, that generally agreed well with previous 14C-based PP estimates in the region. The 14C-PPeqv estimates were 1-1.6 concurrent satellite-based PP estimates along the cruise track. A net community production rate (NCP) of 87 12 mmol O2 m-2 d-1 (62 9 mmol C m-2 d-1) and NCP/GOP of 0.35 0.06 in the mixed layer was estimated from O2/Ar and 17? measurements (61N 26W) during spring bloom conditions in May 2008. Contrastingly, a much lower long-term annual mean NCP or organic carbon export rate of 2.8 2.7 mol C m-2 yr-1 (8 7 mmol C m-2 d-1) and NCP/GOP of 0.07 0.06 at the winter mixed layer depth was estimated from 15 years of surface O2 data in the subpolar N. Atlantic collected during the CARINA program.

  18. Increased nitrogen export from eastern North America to the Atlantic Ocean due to climatic and anthropogenic changes during 1901-2008

    NASA Astrophysics Data System (ADS)

    Yang, Qichun; Tian, Hanqin; Friedrichs, Marjorie A. M.; Hopkinson, Charles S.; Lu, Chaoqun; Najjar, Raymond G.

    2015-06-01

    We used a process-based land model, Dynamic Land Ecosystem Model 2.0, to examine how climatic and anthropogenic changes affected riverine fluxes of ammonium (NH4+), nitrate (NO3-), dissolved organic nitrogen (DON), and particulate organic nitrogen (PON) from eastern North America, especially the drainage areas of the Gulf of Maine (GOM), Mid-Atlantic Bight (MAB), and South Atlantic Bight (SAB) during 1901-2008. Model simulations indicated that annual fluxes of NH4+, NO3-, DON, and PON from the study area during 1980-2008 were 0.019 ± 0.003 (mean ± 1 standard deviation) Tg N yr-1, 0.18 ± 0.035 Tg N yr-1, 0.10 ± 0.016 Tg N yr-1, and 0.043 ± 0.008 Tg N yr-1, respectively. NH4+, NO3-, and DON exports increased while PON export decreased from 1901 to 2008. Nitrogen export demonstrated substantial spatial variability across the study area. Increased NH4+ export mainly occurred around major cities in the MAB. NO3- export increased in most parts of the MAB but decreased in parts of the GOM. Enhanced DON export was mainly distributed in the GOM and the SAB. PON export increased in coastal areas of the SAB and northern parts of the GOM but decreased in the Piedmont areas and the eastern parts of the MAB. Climate was the primary reason for interannual variability in nitrogen export; fertilizer use and nitrogen deposition tended to enhance the export of all nitrogen species; livestock farming and sewage discharge were also responsible for the increases in NH4+ and NO3- fluxes; and land cover change (especially reforestation of former agricultural land) reduced the export of the four nitrogen species.

  19. Large-Scale Ocean Circulation: Deep Circulation and Meridional Overturning

    NASA Astrophysics Data System (ADS)

    Rintoul, Stephen R.

    Roughly half the world ocean volume lies below 2,000m depth. This deep half of the ocean is cold (<3C), indicating that the abyssal ocean is filled with waters that sink in high latitudes, where cold surface waters are found [1]. The deep ocean circulation transports the cold waters that sink in the polar regions throughout the deep ocean basins. The transfer of surface water to the deep ocean must be balanced by an inflow of water in the upper ocean to the deep water formation regions, to conserve mass. The result is an "overturning circulation," in which the export of cold deep waters from the source regions is balanced by a return flow of warmer water in the upper ocean. The large temperature contrast between the upper and lower limbs of the overturning circulation makes this flow pattern an efficient means of transporting heat. The large-scale overturning circulation is the primary means by which the ocean stores and transports quantities of relevance to the Earth's climate system and biogeochemical cycles, including heat, freshwater, carbon, and nutrients. The evolution of climate is therefore influenced strongly by the overturning circulation.

  20. Variation in freshwater input to the Eastern US coastal ecosystem

    NASA Astrophysics Data System (ADS)

    Feng, D.; Yoon, Y.; Beighley, E., II; Hughes, R.; Kimbro, D.

    2014-12-01

    Phragmites is one of the most invasive plants in North American wetlands. Although its spread in coastal marshes has been linked by independent studies to urbanization, eutrophication, and salinity change, there is good evidence that these factors may interactively determine invasion success and in turn, the ecosystem services provided by marshes. We hypothesize that the invasion of Phragmites is linked to changes in freshwater inputs due to climate and/or land use change. El Nino/Southern Oscillation (ENSO), originating in the sea surface temperature anomalies (warm or cold) in the eastern tropical Pacific Ocean, is a notable and prominent signal in inter-annual climatic variation. Recent studies shows that the probability of strong El Nino events may increase in the future. In this study, we will investigate the teleconnections between freshwater inputs to the coastal zone along the eastern U.S. and ENSO indices, and attempt to explore the predictability of temporal and spatial variation of freshwater inputs based on ENSO conditions. To quantify changes in freshwater input in this region, hydrologic modeling, remote sensing and field measurements are combined. The Hillslope River Routing (HRR) model is used to simulate hourly streamflow from all watersheds from southern Florida to northern Maine draining into the Atlantic Ocean. The modeling effort utilizes satellite precipitation (Tropical Rainfall Measuring Mission Product 3B42v7: 2001-current with a 3-hr temporal resolution and 0.25 degree spatial resolution), land surface temperature and vegetation measures (Moderate Resolution Imaging Spectroradiometer, MODIS, products: 2001-current with a monthly temporal resolution and 0.05 degree spatial resolution). To account for land cover change, annual MODIS land cover data and time varying population statics are merged to estimate annual land cover characteristics for each sub-catchment within the study region. Static datasets for soils and ground elevations are used. Daily U.S. Geological Survey streamflow data from major river outlets along the coastline are used for model validation. Annual streamflow is characterized in terms of volume of export to the ocean: as total flow, storm flow and baseflow and used to explore longitudinal discharge patterns along the coastline.

  1. Interannual variations of freshwater in Hornsund

    NASA Astrophysics Data System (ADS)

    Dlven, Knut Ola; Falck, Eva

    2015-04-01

    Hornsund is a fjord situated at the south-west coast of Spitsbergen. The main goal of this study is to calculate and describe the interannual variations of freshwater content in Hornsund. In addition to this, we aim to trace the freshwater sources to the fjord and calculate the fractional contributions from these by using oxygen isotope data. The mixing between these freshwater sources and oceanic waters is described as well as the general summer hydrography of the fjord. Calculation of freshwater content is based on Conductivity-Temperature-Depth data obtained in July of 2001 to 2014. Oxygen isotope data are obtained in Autumn 2013/2014 and Spring 2014. The freshwater in Hornsund is assumed to be provided by either meteoric freshwater sources (glacial melt/precipitation/river-runoff) or the melting of sea ice. Both sources can be produced locally or advected into the fjord. The fraction of the ?O isotope (??O) is an effective tracer for freshwater sources in the Arctic due to the progressive depletion of this isotope in water molecules during poleward atmospheric transport (Ostlund and Hut, 1984). Calculation of fractional contribution from the two freshwater sources is done based on a method presented in Ostlund and Hut (1984), where the mass-balance, salinity-balance and ??O-balance are utilized to calculate the fractions of seawater, meteoric water and sea ice meltwater. Preliminary results show freshwater content varying between 0.211km and 1.068km, based on a reference salinity of 34.2. In Autumn 2013, meteoric water was the largest contributor of freshwater to the fjord. However, there was a significant contribution of sea ice meltwater which had a deeper vertical distribution than the meteoric water. References: H. G. Ostlund and G. Hut. 1984. Arctic Ocean water mass balance from isotope data. Journal of Geophysical Research: Oceans 89(C4):6373-6381

  2. The influence of large-scale environmental changes on carbon export in the North Pacific Ocean using satellite and shipboard data

    NASA Astrophysics Data System (ADS)

    Goes, Joaquim I.; Gomes, Helga do R.; Limsakul, Atsamon; Saino, Toshiro

    2004-01-01

    The subarctic Pacific Ocean experiences strong climate-modulated seasonal, interannual to decadal variations in meteorological and physical oceanographic conditions, which can have a profound influence on biological processes and carbon cycling in the region. Inorganic nitrate, a major nutrient controlling phytoplankton growth, is key to understanding the export of organic matter out of the euphotic zone. Its supply to the region is driven largely by winter convective mixing. Using satellite data for a 5-year period beginning in 1997, we provide evidence of strong interannual variations in the supply of inorganic nitrate and new production in the subarctic Pacific in association with the El-Nio of 1997 and the transition to La-Nia conditions thereafter. These satellite based climatologies allowed us to view and describe large changes in nitrate distribution and new production along the entire breadth of the subarctic Pacific basin. In addition, our accessibility to a 25-year database of shipboard measurements focused primarily in the Oyashio waters, a region representative of the western subarctic Pacific, enabled us to demonstrate that El-Nio/La-Nia changes in this region differed from those observed in the eastern subarctic Pacific. Thus, in addition to the primary motive of verifying the changes that we observed in our satellite-derived maps, this exercise allowed us to obtain a clear picture of the mechanistic connections between the atmosphere and the oceans and the biological response to these changes. The results from this study make a compelling case that the primary driver for the observed interannual variations in biological production in the western subarctic Pacific is the strength of the wintertime monsoonal winds. This anomalous intensification of the southeastward wind stress appears to be particularly strong during El-Nio years when the Aleutian Low intensifies and moves southeastwards, causing disturbances in the pressure gradient between the Siberian high and the Aleutian Low. An abrupt shift in oceanographic conditions follows this change in pressure gradient, among them the most prominent being a reduction in sea surface temperature, a southward migration of the belt of zero wind-stress curl, and the anomalous southward penetration of the Oyashio Current. In tandem, these changes, contribute to an increase in nutrient inputs in winter and a southward displacement of the boundary of the subarctic gyre. The spring following an El-Nio event is characterized by reduced wind stress and a resulting increase in water column stability as well as the elevated solar radiation leads to blooms. Conversely, in the winter of 2000, the subarctic gyre experienced the weakest winds of all 5 years. These weak wind conditions were associated with increased wind speeds in spring of that year and the lowest annual rates of new production of all 5 years.

  3. Greenland Freshwater Input to the North Atlantic

    NASA Astrophysics Data System (ADS)

    Beaird, N.; Straneo, F.

    2014-12-01

    The Greenland Ice Sheet (GrIS) is losing mass at an unprecedented rate. The associated increased freshwater flux directly contributes to sea level rise, but also has dynamical implications for the Atlantic Meridional Overturning Circulation and global climate. The freshwater buoyancy forcing from marine terminating outlet glaciers is distributed throughout the depth of coastal fjords. When coupled with strong fjord stratification, this buoyancy forcing can drive significant water mass transformation (WMT) of subsurface waters in the fjord. The WMT differs substantially from a simple freshwater input to the surface ocean. This often overlooked small-scale overturning has potentially important consequences for the influence of GrIS freshwater on large scale ocean circulation and needs to be accounted for in studies of GrIS impact on the ocean. From ship-based and moored hydrographic measurements in East Greenland (2008 to 2013) we describe the character and temporal variability of meltwater driven WMT. While melting always adds freshwater to the ocean, the corresponding WMT causes a seasonally variable vertical redistribution of heat and salt. Observations show that the seasonal cycle of the WMT lags surface air temperatures by several months. We discuss how the WMT and its timing might impact the boundary current system in East Greenland, and implications for its representation in numerical models and impact on North Atlantic deep convection.

  4. Arctic freshwater synthesis: Introduction

    NASA Astrophysics Data System (ADS)

    Prowse, T.; Bring, A.; Mrd, J.; Carmack, E.

    2015-11-01

    In response to a joint request from the World Climate Research Program's Climate and Cryosphere Project, the International Arctic Science Committee, and the Arctic Council's Arctic Monitoring and Assessment Program, an updated scientific assessment has been conducted of the Arctic Freshwater System (AFS), entitled the Arctic Freshwater Synthesis (AFS?). The major reason for joint request was an increasing concern that changes to the AFS have produced, and could produce even greater, changes to biogeophysical and socioeconomic systems of special importance to northern residents and also produce extra-Arctic climatic effects that will have global consequences. Hence, the key objective of the AFS? was to produce an updated, comprehensive, and integrated review of the structure and function of the entire AFS. The AFS? was organized around six key thematic areas: atmosphere, oceans, terrestrial hydrology, terrestrial ecology, resources and modeling, and the review of each coauthored by an international group of scientists and published as separate manuscripts in this special issue of Journal of Geophysical Research-Biogeosciences. This AFS?Introduction reviews the motivations for, and foci of, previous studies of the AFS, discusses criteria used to define the domain of the AFS, and details key characteristics of the definition adopted for the AFS?.

  5. Temporal variability of fluxes of eolian-transported freshwater diatoms, phytoliths, and pollen grains off Cape Blanc as reflection of land-atmosphere-ocean interactions in northwest Africa

    NASA Astrophysics Data System (ADS)

    Romero, Oscar E.; Dupont, Lydie; Wyputta, Ulrike; Jahns, Susanne; Wefer, Gerold

    2003-05-01

    Fluxes of airborne freshwater diatoms (FD), phytoliths (PH), and pollen grains (PO) collected with sediment traps off Cape Blanc, northwest Africa, from 1988 till 1991 are presented. Both continental rainfall variations and wind mean strength and direction play a key role in the temporal fluctuations of the fluxes of eolian traces in the pelagic realm. Drier conditions in Northern Africa in 1987 could have preceded the high lithogenic input and moderate FD flux in 1988. The PH peak in summer 1988 was probably caused by increased wind velocity. Wetter rainy seasons of 1988/89 might have promoted a significant pollen production in summer 1989, and FD in late 1989 and early 1990, as well as contributed to the reduction of the lithogenic flux in 1989/90. Decreased fluxes of FD, PH and PO, and higher contribution of the 6-11 ?m lithogenic fraction in 1991 would mainly reflect minor intensity and decreased amount of continental trade winds. Air-mass backward trajectories confirm that the Saharan Air Layer is predominantly involved in the spring/summer transport. Trade winds play a decisive role in the fall/winter months, but also contribute to the transport during late spring/summer. Origin of wind trajectories does not support a direct relationship between transporting wind-layers and material source areas in Northern Africa. High winter fluxes of eolian tracers and high amount of trade winds with continental origin in summer warn against a simplistic interpretation of the seasonal eolian signal preserved in the sediments off Cape Blanc, and the wind layer involved in its transport.

  6. Export Fluxes of Dissolved Organic Carbon From the Yukon River

    NASA Astrophysics Data System (ADS)

    Guo, L.; Cai, Y.; Belzile, C.; MacDonald, R.

    2005-12-01

    Quantitative determination of export fluxes of carbon species through Arctic rivers is required to constrain the carbon budget in the Arctic Ocean and to understand the biogeochemical consequence of climate change in Northern drainage basins. In order to quantify the annual riverine export flux from the Yukon River, monthly or bimonthly water samples were collected at Pilot Station from July 2004 to July 2005 and analyzed for concentrations of dissolved organic carbon (DOC), particulate organic carbon (POC) and dissolved inorganic carbon (DIC). Concentration of DOC varied from 182 to 1683 uM (average 441 uM), with the highest concentration during river ice opening and the lowest in April under the ice. In contrast, DIC concentration increased from ice opening in May (1178 uM) to winter frozen season (2128 uM), with an average of 1588 uM. In addition to the DOC maximum during ice opening, an elevated DOC concentration was observed during the early stage of river ice formation, suggesting the rejection of DOC from ice during its formation. There was a positive correlation of DOC with freshwater flow rate whereas DIC correlated negatively with flow, indicating a hydrological control on both components but different source terms and transport mechanisms. Integrated annual export flux during 2004/2005 was 2.78x1012 g-C/y for DOC and 4.53x1012 g-C/y for DIC. Within the annual fluxes, only 5% of DOC and 17% of DIC were exported during the winter period when the river was frozen over. Long-term observations of DOC and DIC together with their molecular and isotopic signatures are needed to understand how the Yukon River Basin responds to a changing climate.

  7. Freshwater ecosystems

    SciTech Connect

    Straskraba, M.; Gnauck, A.H.

    1985-01-01

    Ecosystem analysis and ecological modelling is a rapidly developing interdisciplinary branch of science used in theoretical developments in ecology and having practical applications in environmental protection. In this book, the authors introduce new holistic, particularly cybernetic, concepts into ecosystem theory and modelling, and provide a concise treatment of mathematical modelling of freshwater ecosystems which covers methods, subsystem models, applications and theoretical developments. Part 1 begins with a brief introduction to the principles of systems theory and their applications to ecosystems, and provides a summary of various methods of systems analysis. In Part 11 emphasis is laid on the pelagic processes in standing water, characterised by relatively uninvolved structures from which models can be readily developed. Part 111 describes applications of the technique of modelling to solutions of theoretical and practical problems, with different modelling methods and objectives being used in the various chapters. More recent developments in the methods and theory of ecosystem modelling are covered in Part 1V which also includes a discussion of future trends.

  8. A subtropical fate awaited freshwater discharged from glacial Lake Agassiz

    SciTech Connect

    Condron, Alan; Winsor, Peter

    2011-02-10

    The 8.2 kyr event is the largest abrupt climatic change recorded in the last 10,000 years, and is widely hypothesized to have been triggered by the release of thousands of kilometers cubed of freshwater into the North Atlantic Ocean. Using a high-resolution (1/6°) global, ocean-ice circulation model we present an alternative view that freshwater discharged from glacial Lake Agassiz would have remained on the continental shelf as a narrow, buoyant, coastal current, and would have been transported south into the subtropical North Atlantic. The pathway we describe is in contrast to the conceptual idea that freshwater from this lake outburst spread over most of the sub-polar North Atlantic, and covered the deep, open-ocean, convection regions. This coastally confined freshwater pathway is consistent with the present-day routing of freshwater from Hudson Bay, as well as paleoceanographic evidence of this event. In this study, using a coarse-resolution (2.6°) version of the same model, we demonstrate that the previously reported spreading of freshwater across the sub-polar North Atlantic results from the inability of numerical models of this resolution to accurately resolve narrow coastal flows, producing instead a diffuse circulation that advects freshwater away from the boundaries. To understand the climatic impact of freshwater released in the past or future (e.g. Greenland and Antarctica), the ocean needs to be modeled at a resolution sufficient to resolve the dynamics of narrow, coastal buoyant flows.

  9. Dom Export from Coastal Temperate Bog Forest Watersheds to Marine Ecosystems: Improving Understanding of Watershed Processes and Terrestrial-Marine Linkages on the Central Coast of British Columbia

    NASA Astrophysics Data System (ADS)

    Oliver, A. A.; Giesbrecht, I.; Tank, S. E.; Hunt, B. P.; Lertzman, K. P.

    2014-12-01

    The coastal temperate bog forests of British Columbia, Canada, export high amounts of dissolved organic matter (DOM) relative to the global average. Little is known about the factors influencing the quantity and quality of DOM exported from these forests or the role of this terrestrially-derived DOM in near-shore marine ecosystems. The objectives of this study are to better understand patterns and controls of DOM being exported from bog forest watersheds and its potential role in near-shore marine ecosystems. In 2013, the Kwakshua Watershed Ecosystems Study at Hakai Beach Institute (Calvert Island, BC) began year-round routine collection and analysis of DOM, nutrients, and environmental variables (e.g. conductivity, pH, temperature, dissolved oxygen) of freshwater grab samples from the outlets of seven watersheds draining directly to the ocean, as well as near-shore marine samples adjacent to freshwater outflows. Dissolved organic carbon (DOC) varied across watersheds (mean= 11.45 mg L-1, sd± 4.22) and fluctuated synchronously with seasons and storm events. In general, higher DOC was associated with lower specific UV absorbance (SUVA254; mean= 4.59 L mg-1 m-1, sd± 0.55). The relationship between DOC and SUVA254 differed between watersheds, suggesting exports in DOM are regulated by individual watershed attributes (e.g. landscape classification, flow paths) as well as precipitation. We are using LiDAR and other remote sensing data to examine watershed controls on DOC export. At near-shore marine sites, coupled CTD (Conductivity Temperature Depth) and optical measures (e.g. spectral slopes, slope ratios (SR), EEMs), showed a clear freshwater DOM signature within the system following rainfall events. Ongoing work will explore the relationship between bog forest watershed attributes and DOM flux and composition, with implications for further studies on biogeochemical cycling, carbon budgets, marine food webs, and climate change.

  10. Impact of natural (waves and currents) and anthropogenic (trawl) resuspension on the export of particulate matter to the open ocean: Application to the Gulf of Lion (NW Mediterranean)

    NASA Astrophysics Data System (ADS)

    Ferr, B.; Durrieu de Madron, X.; Estournel, C.; Ulses, C.; Le Corre, G.

    2008-08-01

    Modern sediment deposits on continental margins form a vast reservoir of particulate matter that is regularly affected by resuspension processes. Resuspension by bottom trawling on shelves with strong fishing activity can modify the scale of natural disturbance by waves and currents. Recent field data show that the impact of bottom trawls on fine sediment resuspension per unit surface is comparable with that of the largest storms. We assessed the impact of both natural and anthropogenic processes on the dispersal of riverborne particles and shelf sediments on the Gulf of Lion shelf. We performed realistic numerical simulations of resuspension and transport forced by currents and waves or by a fleet of bottom trawlers. Simulations were conducted for a 16-month period (January 1998-April 1999) to characterise the seasonal variability. The sediment dynamics takes into account bed armoring, ripple geometry and the cohesive and non-cohesive characteristics of the sediments. Essential but uncertain parameters (clay content, erosion fluxes and critical shear stress for cohesive sediment) were set with existing data. Resuspension by waves and currents was controlled by shear stress, whereas resuspension by trawls was controlled by density and distribution of the bottom trawler fleet. Natural resuspension by waves and currents mostly occurred during short seasonal episodes, and was concentrated on the inner shelf. Trawling-induced resuspension, in contrast, occurred regularly throughout the year and was concentrated on the outer shelf. The total annual erosion by trawls (5.610 6 t y -1, t for metric tonnes) was four orders of magnitude lower than the erosion induced by waves and currents (35.310 9 t y -1). However the net resuspension (erosion/deposition budget) for trawling (0.410 6 t y -1) was only one order of magnitude lower than that for waves and currents (9.210 6 t y -1). Off-shelf export concerned the finest fraction of the sediment (clays and fine silts) and took place primarily at the southwestern end of the Gulf. Off-shelf transport was favoured during the winter 1999 by a very intense episode of dense shelf water cascading. Export of sediment resuspended by trawls (0.410 6 t y -1) was one order of magnitude lower than export associated with natural resuspension (8.510 6 t y -1). Trawling-induced resuspension is thought to represent one-third of the total export of suspended sediment from the shelf. A simulation combining both resuspension processes reveals no significant changes in resuspension and export rates compared with the sum of each individual process, suggesting the absence of interference between both processes.

  11. The interaction between sea ice and salinity-dominated ocean circulation: implications for halocline stability and rapid changes of sea ice cover

    NASA Astrophysics Data System (ADS)

    Jensen, Mari F.; Nilsson, Johan; Nisancioglu, Kerim H.

    2016-02-01

    Changes in the sea ice cover of the Nordic Seas have been proposed to play a key role for the dramatic temperature excursions associated with the Dansgaard-Oeschger events during the last glacial. In this study, we develop a simple conceptual model to examine how interactions between sea ice and oceanic heat and freshwater transports affect the stability of an upper-ocean halocline in a semi-enclosed basin. The model represents a sea ice covered and salinity stratified Nordic Seas, and consists of a sea ice component and a two-layer ocean. The sea ice thickness depends on the atmospheric energy fluxes as well as the ocean heat flux. We introduce a thickness-dependent sea ice export. Whether sea ice stabilizes or destabilizes against a freshwater perturbation is shown to depend on the representation of the diapycnal flow. In a system where the diapycnal flow increases with density differences, the sea ice acts as a positive feedback on a freshwater perturbation. If the diapycnal flow decreases with density differences, the sea ice acts as a negative feedback. However, both representations lead to a circulation that breaks down when the freshwater input at the surface is small. As a consequence, we get rapid changes in sea ice. In addition to low freshwater forcing, increasing deep-ocean temperatures promote instability and the disappearance of sea ice. Generally, the unstable state is reached before the vertical density difference disappears, and the temperature of the deep ocean do not need to increase as much as previously thought to provoke abrupt changes in sea ice.

  12. 48 CFR 52.247-51 - Evaluation of Export Offers.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 48 Federal Acquisition Regulations System 2 2011-10-01 2011-10-01 false Evaluation of Export....247-51 Evaluation of Export Offers. As prescribed in 47.305-6(e), insert the following provision: Evaluation of Export Offers (JAN 2001) (a) Port handling and ocean chargesother than DOD water...

  13. 48 CFR 52.247-51 - Evaluation of Export Offers.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 48 Federal Acquisition Regulations System 2 2010-10-01 2010-10-01 false Evaluation of Export....247-51 Evaluation of Export Offers. As prescribed in 47.305-6(e), insert the following provision: Evaluation of Export Offers (JAN 2001) (a) Port handling and ocean chargesother than DOD water...

  14. Aquimixticola soesokkakensis gen. nov., sp. nov., a novel lipolytic alphaproteobacterium isolated from the junction between the ocean and a freshwater spring, and reclassification of Roseovarius marinus as Pacificibacter marinus comb. nov. and emended description of the genus Pacificibacter.

    PubMed

    Park, Sooyeon; Kang, Chul-Hyung; Park, Ji-Min; Yoon, Jung-Hoon

    2014-10-01

    A Gram-negative, aerobic, non-flagellated and rod-shaped or ovoid bacterial strain, designated DSSK2-3(T), was isolated from the junction between the ocean and a freshwater spring at Jeju island, South Korea. Strain DSSK2-3(T) was found to grow optimally at 30 °C, at pH 7.0-8.0 and in the presence of 2.0-3.0% (w/v) NaCl. Neighbour-joining and maximum-likelihood phylogenetic trees based on 16S rRNA gene sequences revealed that strain DSSK2-3(T) joins the cluster comprising the type strains of Pacificibacter maritimus and Roseovarius marinus, with which it exhibited the highest sequence similarity values of 96.04 and 95.75%, respectively. Sequence similarities to the type strains of other recognized species were <95.74%. Strain DSSK2-3(T) was found to contain Q-10 as the predominant ubiquinone and C(18:1) ω7c as the major fatty acid. The polar lipid profile of strain DSSK2-3(T) was found to contain phosphatidylglycerol, an unidentified lipid and an unidentified aminolipid as major components, which distinguished the strain from those of phylogenetically related taxa. The DNA G+C content of strain DSSK2-3(T) was determined to be 60.8 mol%. On the basis of the phylogenetic data and the chemotaxonomic and other phenotypic properties, strain DSSK2-3(T) is considered to represent a new genus and species within the class Alphaproteobacteria, for which the name Aquimixticola soesokkakensis gen. nov., sp. nov. is proposed. The type strain of A. soesokkakensis is DSSK2-3(T) (=KCTC 42137(T) = CECT 8620(T)). In this study, it is also proposed that R. marinus should be reclassified as a member of the genus Pacificibacter and the description of the genus Pacificibacter is emended. PMID:25052535

  15. 76 FR 38620 - International Fisheries; Atlantic Highly Migratory Species; Bluefin Tuna Import, Export, Re-Export

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-01

    ...; Bluefin Tuna Import, Export, Re-Export AGENCY: National Marine Fisheries Service (NMFS), National Oceanic... fish are tagged) (73 FR 31380, June 2, 2008). Improperly documented bluefin tuna may be prohibited from... respect to any import of Atlantic bluefin tuna harvested by Libyan vessels in 2011, as these shipments...

  16. Linking Ice Sheet Freshwater Discharge and Marine production in Greenland via Fiord Circulation. 'FreshLink', an Interdisciplinary Project Involving Researchers from Multiple Countries.

    NASA Astrophysics Data System (ADS)

    Bggild, C. E.; Rysgaard, S.; Mortensen, J.; Kallenborn, R.; Truffer, M.; Forsberg, R.; Ahlstrm, A. P.; Petersen, D.

    2008-12-01

    This interdisciplinary and international project has recently been initiated mainly with IPY funding from Denmark and Greenland. In short the project investigates the linkage between ice sheet freshwater release to a fiord near Nuuk (South-western Greenland) and the resulting fiord circulation. The low density melt water draining into the innermost of the long fiord forms a brackish outward sloping top layer, which exits the fiord and is balanced by entrance of nutritious salty oceanic water below. Such nutritious water, in turn, favors marine production in the fiord. The perspectives of a warmer climate, where more ice sheet melt water will increase the marine production, is of vital interest to investigate for the Greenland society because the present export from the country is totally dominated by living resources of the oceans. This interdisciplinary research project involves scientists from Greenland, Norway, Denmark and USA. Scientific disciplines presently covered are; marine ecology (biological production), cryospheric sciences (ice sheet and snow-water release), pollution chemistry (separating present from ancient precipitation), marine geology (history of freshwater input), oceanography (fiord circulation), geodesy (cryospheric elevation changes), and hydrology (land runoff). First field results will be presented together with the perspectives for linking each fresh water component coming from land and ice to the observed freshwater budget in the fiord.

  17. Greenland Ice Sheet Meltwater Export and River Discharge

    NASA Astrophysics Data System (ADS)

    Rennermalm, A. K.; Tedesco, M.; Mote, T. L.; Overeem, I.; Mikkelsen, A. B.; Hasholt, B.

    2014-12-01

    The Greenland ice sheet supplies massive amounts of freshwater and sediments to surrounding oceans, contributing to global sea level rise and influencing marine ecosystems. A large portion of this meltwater runoff flows through rivers draining the entire perimeter of the ice sheet. These unique river systems are characterized by strong seasonality, high sediment loads due to glacial erosion, and variable basin size and hypsometry over a melt season, during which the melting front propagates upwards and engages an increasingly larger drainage basin area. Other sources of Greenland streamflow include runoff from tundra areas, peripheral glaciers and ice caps. Despite the uniqueness and importance of Greenland surface streams, a comprehensive, comparative study of these systems has not been made. Here, we present an investigation of these systems and analyze their role in the total Greenland meltwater export to the ocean. River catchment areas are identified by analyzing high-resolution digital elevation models of ice sheet surface topography. Discharge from individual rivers are derived from the regional surface mass balance model Modèle Atmosphérique Régional (MAR). Our inventory of Greenland Rivers' hydrological regime, characteristics, and emerging trends provides insights into the current and future state of Greenland streamflow.

  18. A 50% increase in the amount of terrestrial particles delivered by the Mackenzie River into the Beaufort Sea (Canadian Arctic Ocean) over the last 10 years

    NASA Astrophysics Data System (ADS)

    Doxaran, D.; Devred, E.; Babin, M.

    2015-01-01

    Global warming has a significant impact at the regional scale on the Arctic Ocean and surrounding coastal zones (i.e., Alaska, Canada, Greenland, Norway and Russia). The recent increase in air temperature has resulted in increased precipitations along the drainage basins of Arctic Rivers. It has also directly impacted land and seawater temperatures with the consequence of melting the permafrost and sea-ice. An increase in freshwater discharge by main Arctic rivers has been clearly identified in time series of field observations. The freshwater discharge of the Mackenzie River has increased by 25% since 2003. This may have increased the mobilization and transport of various dissolved and particulate substances, including organic carbon, as well as their export to the ocean. The release from land to the ocean of such organic material, which was sequestered as frozen since the last glacial maximum, may significantly impact the Arctic Ocean carbon cycle as well as marine ecosystems. In this study we use 11 years of ocean-colour satellite data and field observations collected in 2009 to estimate the amount of terrestrial suspended solids and particulate organic carbon delivered by the Mackenzie River into the Beaufort Sea (Arctic Ocean). Our results show that during the summer period the concentration of suspended solids at the river mouth, in the delta zone and in the river plume has increased by 46, 71 and 33%, respectively, since 2003. Combined with the variations observed in the freshwater discharge, this corresponds to a more than 50% increase in the particulate (terrestrial suspended particles and organic carbon) export from the Mackenzie River into the Beaufort Sea.

  19. A 50 % increase in the mass of terrestrial particles delivered by the Mackenzie River into the Beaufort Sea (Canadian Arctic Ocean) over the last 10 years

    NASA Astrophysics Data System (ADS)

    Doxaran, D.; Devred, E.; Babin, M.

    2015-06-01

    Global warming has a significant impact on the regional scale on the Arctic Ocean and surrounding coastal zones (i.e., Alaska, Canada, Greenland, Norway and Russia). The recent increase in air temperature has resulted in increased precipitation along the drainage basins of Arctic rivers. It has also directly impacted land and seawater temperatures with the consequence of melting permafrost and sea ice. An increase in freshwater discharge by main Arctic rivers has been clearly identified in time series of field observations. The freshwater discharge of the Mackenzie River has increased by 25% since 2003. This may have increased the mobilization and transport of various dissolved and particulate substances, including organic carbon, as well as their export to the ocean. The release from land to the ocean of such organic material, which has been sequestered in a frozen state since the Last Glacial Maximum, may significantly impact the Arctic Ocean carbon cycle as well as marine ecosystems. In this study we use 11 years of ocean color satellite data and field observations collected in 2009 to estimate the mass of terrestrial suspended solids and particulate organic carbon delivered by the Mackenzie River into the Beaufort Sea (Arctic Ocean). Our results show that during the summer period, the concentration of suspended solids at the river mouth, in the delta zone and in the river plume has increased by 46, 71 and 33%, respectively, since 2003. Combined with the variations observed in the freshwater discharge, this corresponds to a more than 50% increase in the particulate (terrestrial suspended particles and organic carbon) export from the Mackenzie River into the Beaufort Sea.

  20. Greenland Ice Sheet nutrient export: Towards a reaction-transport model of fjord dynamics

    NASA Astrophysics Data System (ADS)

    Crosby, James; Arndt, Sandra; Wadham, Jemma; Bingham, Rory

    2015-04-01

    Glacial runoff has the potential to deliver large quantities of dissolved and particulate bioavailable nutrients to surrounding marine environments. The marine waters bordering the Greenland Ice Sheet (GrIS) host some of the most productive ecosystems in the world, and possess high socio-economic value from fisheries. Furthermore, the productivity of phytoplankton in the North Atlantic sequesters CO2 from the atmosphere with a potentially important effect on the global coastal ocean CO2 budget. Providing a link between glacier and coastal ocean, fjords are critical components of the marine coastal system in this region, acting as both transfer routes and sinks for glacial nutrient export. As such they have the potential to act as significant biogeochemical processors, yet are currently underexplored. We propose to close this knowledge gap by developing a coupled 2D physical-biogeochemical model of the Godthbsfjord system to quantitatively assess the impact of nutrients exported from the GrIS on fjord primary productivity and biogeochemical dynamics. Here, we present the first results of the hydrodynamic model. Hydrodynamic circulation patterns and freshwater transit times are explored to provide a first understanding of the glacier-fjord-ocean continuum. The hydrodynamic model will be dynamically coupled to a biogeochemical model with the view to providing a comprehensive understanding of the fate of nutrients exported from the GrIS. This will be extended to address the future sensitivity of these coastal systems to a warming climate, knowledge of which is critical when assessing the role of these dynamic and unique environments.

  1. Forcing of the deep ocean circulation in simulations of the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Schmittner, A.; Meissner, K. J.; Eby, M.; Weaver, A. J.

    2002-05-01

    From the interpretation of different proxy data it is widely believed that the North Atlantic thermohaline circulation during the maximum of the last ice age ~21,000 years ago was considerably weaker than today. Recent equilibrium simulations with a coupled ocean-atmosphere-sea ice model successfully simulated a reduction in North Atlantic Deep Water (NADW) formation consistent with reconstructions. Here we examine the influence of different air-sea fluxes on simulated changes in the deep ocean circulation between the Last Glacial Maximum and present day. We find that changes in the oceanic surface freshwater fluxes are the dominant forcing mechanism for the reduced Atlantic overturning. Diminished export of freshwater out of the Atlantic drainage basin through the atmosphere decreases surface salinities in the North Atlantic, leading to less NADW formation in the colder climate. Changes in heat fluxes, which lead to increased sea surface densities in the North Atlantic and therefore to an enhanced overturning, are of secondary importance. Wind stress variations seem to play a negligible role. The degree to which the Atlantic freshwater export and hence the NADW formation are reduced depends on the formulation of the atmospheric hydrological cycle and on the strength of the overturning in the present-day simulation. Simulated changes in sea surface properties for a large variety of overturning strengths are compared with different reconstruction data sets. The results depend strongly on the data set used. Sea surface temperature reconstructions from Climate: Long-Range Investigation, Mapping, and Prediction (CLIMAP) and earlier salinity reconstructions based on planktonic foraminifera are most consistent with a significant reduction of the circulation, while recent reconstructions using dinocyst assemblages allow no unequivocal conclusion.

  2. Confluentimicrobium lipolyticum gen. nov., sp. nov., a novel lipolytic alphaproteobacterium isolated from the junction between the ocean and a freshwater spring, and emended description of Actibacterium mucosum Lucena et al. 2012.

    PubMed

    Park, Sooyeon; Park, Ji-Min; Kang, Chul-Hyung; Yoon, Jung-Hoon

    2014-11-01

    A Gram-negative, aerobic, non-flagellated and coccoid, ovoid or rod-shaped bacterial strain, designated SSK1-4(T), was isolated from the junction between the ocean and a freshwater spring at Jeju island, South Korea. Strain SSK1-4(T) was found to grow optimally at 30 °C, at pH 7.0-8.0 and in the presence of 2.0 % (w/v) NaCl. In the neighbour-joining, maximum-likelihood and maximum-parsimony phylogenetic trees based on 16S rRNA gene sequences, strain SSK1-4(T) was found to form an evolutionary lineage independent of those of other genera within the family Rhodobacteraceae. Strain SSK1-4(T) exhibited the highest 16S rRNA gene sequence similarity values to the type strains of Ruegeria lacuscaerulensis (94.99 %), Ruegeria atlantica (94.98 %) and Rhodovulum marinum (94.97 %). Sequence similarities to the type strains of other recognized species were less than 94.87 %. Strain SSK1-4(T) was found to contain Q-10 as the predominant ubiquinone and C18:1 ω7c and cyclo-C19:0 ω8c as the major fatty acids. The polar profile of strain SSK1-4(T) was found to contain phosphatidylglycerol, sulfoquinovosyldiacylglycerol, an unidentified lipid and an unidentified aminolipid as major components, which distinguish it from those of the phylogenetically related taxa. The DNA G+C content of strain SSK1-4(T) was determined to be 58.4 mol%. On the basis of the phylogenetic data and the chemotaxonomic and other phenotypic properties, strain SSK1-4(T) is considered to represent a new genus and species within the class Alphaproteobacteria, for which the name Confluentimicrobium lipolyticum gen. nov., sp. nov. is proposed. The type strain of C. lipolyticum is SSK1-4(T) (=KCTC 42136(T) = CECT 8621(T)). In addition, an emended description of Actibacterium mucosum Lucena et al. 2012 is also proposed. PMID:25150887

  3. The Central American Seaway and the Late Neogene ocean conveyor belt

    NASA Astrophysics Data System (ADS)

    Schneider, Birgit; Krebs-Kanzow, Uta; Park, Wonsun

    2013-04-01

    'The great ocean conveyor belt' depicts the large scale exchange of water mass properties between today's oceans. Over the past million years the tectonic evolution of ocean passages altered this pan-oceanic communication. The last such tectonic transformation was the closure of the Central American Seaway (CAS) which represented a low latitude gateway between Pacific and Atlantic prior to 4 million years ago. We use a coupled general circulation model and configure the topography for the past. The Central American Seaway modifies the global ocean circulation and the ocean conveyor belt which implies drastic changes in water mass properties and inter basin heat and freshwater transports. Compared to an experiment with modern basin geometry, a 1000-meter deep passage at the location of today's Isthmus of Panama results in a fundamental change in the warm water route of the conveyor belt while the cold path remains qualitatively unchanged. A transport of 10 Sv from Pacific to Atlantic is associated with the meridional transport in the South Atlantic changing from 10Sv northward to 2 Sv southward. Both Indonesian throughflow and export of warm water from the Indian Ocean across 30S are reduced by about 7 Sv. Analysing transports in density classes we are able to propose a sketch of the late Neogene conveyor belt.

  4. Changes in the North Pacific Ocean biological pump from MIS 5e to MIS 3

    NASA Astrophysics Data System (ADS)

    Swann, G.

    2009-12-01

    Diatom isotope records from the North Pacific Ocean provide an important means by which to further investigate past climatic and oceanographic changes in a region marked by depleted concentrations of foraminifera and other carbonates within the sedimentary record. Combined measurements of diatom oxygen (?18Odiatom) and silicon (?30Sidiatom) from ODP Site 882 indicate significant changes in both freshwater input to the region and the biological pump between MIS 5e and MIS 3. Unchanging values of ?18Odiatom and low/moderate values of ?30Sidiatom suggest relatively stable oceanographic conditions during MIS 5e until a marked, freshwater induced, decrease in ?18Odiatom at the MIS 5e/d boundary. Increases in opal concentrations and ?30Sidiatom to values of 1.2-1.3 between MIS 5d and MIS 5b indicate a subsequent increase in nutrient utilisation and export production. With these changes coinciding with a progressive long-term decrease in atmospheric pCO2, the North West Pacific Ocean may have assisted in lowering pCO2 and driving the climatic system into the glacial conditions that prevailed during the last glacial. Subsequent changes in ?30Sidiatom/nutrient utilisation from MIS 5a to MIS 3 covary with ?18Odiatom inferred changes in freshwater input to the region, indicating a long-term regulation of the regional biological pump via a strengthening/weakening of the halocline stratification.

  5. A model-data comparison of δ13C in the glacial Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Hesse, T.; Butzin, M.; Bickert, T.; Lohmann, G.

    2011-09-01

    We compare a compilation of 220 sediment core δ13C data from the glacial Atlantic Ocean with three-dimensional ocean circulation simulations including a marine carbon cycle model. The carbon cycle model employs circulation fields which were derived from previous climate simulations. All sediment data have been thoroughly quality controlled, focusing on epibenthic foraminiferal species (such as Cibicidoides wuellerstorfi or Planulina ariminensis) to improve the comparability of model and sediment core carbon isotopes. The model captures the general δ13C pattern indicated by present-day water column data and Late Holocene sediment cores but underestimates intermediate and deep water values in the South Atlantic. The best agreement with glacial reconstructions is obtained for a model scenario with an altered freshwater balance in the Southern Ocean that mimics enhanced northward sea ice export and melting away from the zone of sea ice production. This results in a shoaled and weakened North Atlantic Deep Water flow and intensified Antarctic Bottom Water export, hence confirming previous reconstructions from paleoproxy records. Moreover, the modeled abyssal ocean is very cold and very saline, which is in line with other proxy data evidence.

  6. A subtropical fate awaited freshwater discharged from glacial Lake Agassiz

    DOE PAGESBeta

    Condron, Alan; Winsor, Peter

    2011-02-10

    The 8.2 kyr event is the largest abrupt climatic change recorded in the last 10,000 years, and is widely hypothesized to have been triggered by the release of thousands of kilometers cubed of freshwater into the North Atlantic Ocean. Using a high-resolution (1/6°) global, ocean-ice circulation model we present an alternative view that freshwater discharged from glacial Lake Agassiz would have remained on the continental shelf as a narrow, buoyant, coastal current, and would have been transported south into the subtropical North Atlantic. The pathway we describe is in contrast to the conceptual idea that freshwater from this lake outburstmore » spread over most of the sub-polar North Atlantic, and covered the deep, open-ocean, convection regions. This coastally confined freshwater pathway is consistent with the present-day routing of freshwater from Hudson Bay, as well as paleoceanographic evidence of this event. In this study, using a coarse-resolution (2.6°) version of the same model, we demonstrate that the previously reported spreading of freshwater across the sub-polar North Atlantic results from the inability of numerical models of this resolution to accurately resolve narrow coastal flows, producing instead a diffuse circulation that advects freshwater away from the boundaries. To understand the climatic impact of freshwater released in the past or future (e.g. Greenland and Antarctica), the ocean needs to be modeled at a resolution sufficient to resolve the dynamics of narrow, coastal buoyant flows.« less

  7. MODIFICATION OF PHOSPHORUS EXPORT FROM A CATCHMENT BY FLUVIAL SEDIMENT PHOSPHORUS INPUTS

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Phosphorus (P) export from agricultural watersheds can accelerate freshwater eutrophication. Landscape-based remedial measures can reduce edge-of-field P losses. However stream channel hydraulics and fluvial sediment properties can modify the forms and amounts of P exported by the time it reaches th...

  8. Evolution of the Freshwater Eels

    NASA Astrophysics Data System (ADS)

    Aoyama, Jun; Tsukamoto, Katsumi

    The freshwater anguillid eels have an unusual life history and world-wide distribution. Questions about the phylogenetic relationships of this group and how their long spawning migrations and larval phase may contribute to their global distribution have not been addressed. This paper is first presentation of molecular phylogeny of Anguilla species, and based on this phylogenetic tree we suggest new aspect of the evolution of this group. Namely, ancestral eels originated during the Eocene or earlier, in the western Pacific Ocean near present-day Indonesia. A group derived from this ancestor dispersed westward, probably by larval transport in the global circum-equatorial current through the northern edge of the Tethys Sea. This group split into the ancestor of the European and American eels, which entered into the Atlantic Ocean, and a second group, which dispersed southward and split into the east African species and Australian species. Thus the world-wide distribution of the eel family can be understood from knowledge of continental drift, ocean currents, a specialized larva and evolutionary forces favoring dispersal and speciation of segregated gene pool.

  9. Speciation and dynamics of dissolved inorganic nitrogen export in the Danshui River, Taiwan

    NASA Astrophysics Data System (ADS)

    Lee, T.-Y.; Shih, Y.-T.; Huang, J.-C.; Kao, S.-J.; Shiah, F.-K.; Liu, K.-K.

    2014-10-01

    Human-induced excess nitrogen outflowing from land through rivers to oceans has resulted in serious impacts on terrestrial and coastal ecosystems. Oceania, which occupies < 2.5% of the global land surface, delivers 12% of the freshwater and dissolved materials to the ocean on a global scale. However, there are few empirical data sets on riverine dissolved inorganic nitrogen (DIN) fluxes in the region, and their dynamics are poorly understood. In this study, a river monitoring network covering different types of land uses and population densities was implemented to investigate the mechanism of DIN export. The results show that DIN concentration/yield varied from ∼20 μM/∼300 kg-N km-2 yr-1 to ∼378 μM/∼10 000 kg-N km-2 yr-1 from the relatively pristine headwaters to the populous estuary. Agriculture and population density control DIN export in less densely populated regions and urban areas, respectively, and runoff controls DIN at the watershed scale. Compared to documented estimates from global models, the observed DIN export from the Danshui River is 2.3 times larger, which results from the region-specific response of DIN yield to dense population and abundant runoff. The dominating DIN species change gradually from NO3- in the headwaters (∼97%) to NH4+ in the estuary (∼60%) following the urbanization gradient. The prominent existence of NH4+ is probably the result of the anaerobic water body and short residence time, unlike in large river basins. Given the analogous watershed characteristics of the Danshui River to the rivers in Oceania, our study could serve as a first example to examine riverine DIN fluxes in Oceania.

  10. Greater diversification of freshwater than marine parasites of fish.

    PubMed

    Poulin, Robert

    2016-04-01

    The species richness of freshwater environments is disproportionately high compared with that of the oceans, given their respective sizes. If diversification rates are higher in freshwaters because they are isolated and heterogeneous, this should apply to parasites as well. Using 14 large datasets comprising 677 species of freshwater and marine fish, the hypothesis that freshwater parasites experience higher rates of diversification than marine ones is tested by contrasting the relative numbers of species per parasite genus between the regional endohelminth faunas of fish in both environments. The relationship between the number of parasite genera and the number of parasite species per host was well described by a power function, in both environments; although the exponent of this function was slightly lower for freshwater parasite faunas than marine ones, the difference was not significant. However, the ratio between the number of parasite species and the number of parasite genera per host species was significantly higher in freshwater fish than in marine ones. These findings suggest fundamental differences between the way parasite faunas diversify in freshwater versus marine habitats, with the independent evolution of conspecific parasite populations in isolated host populations being a more common phenomenon in freshwater environments. PMID:26802461

  11. Freshwater mussels of Florida

    USGS Publications Warehouse

    Williams, James D.; Butler, Robert S.; Warren, Gary L.; Johnson, Nathan A.

    2014-01-01

    An exhaustive guide to all aspects of the freshwater mussel fauna in Florida,Freshwater Mussels of Floridacovers the ecology, biology, distribution, and conservation of the many species of bivalve mollusks in the Sunshine State. In the past three decades, researchers, the public, businesses that depend on wildlife, and policy makers have given more attention to the threatened natural diversity of the Southeast, including freshwater mussels. This compendium meets the increasingly urgent need to catalog this imperiled group of aquatic organisms in the United States.

  12. Aquatic carbon export from peatland catchments recently undergone wind farm development

    NASA Astrophysics Data System (ADS)

    Smith, Ben; Waldron, Susan; Henderson, Andrew; Flowers, Hugh; Gilvear, David

    2013-04-01

    Scotland's peat landscapes are desirable locations for wind-based renewables due to high wind resources and low land use pressures in these areas. The environmental impact of sitting wind-based renewables on peats however, is unknown. Globally, peatlands are important terrestrial carbon stores. Given the topical nature of carbon-related issues, e.g. global warming and carbon footprints, it is imperative we help mitigate their degradation and maintain carbon sequestration. To do so, we need to better understand how peatland systems function with regards to their carbon balance (export versus sequestration) so we can assess their resilience and adaptation to hosting land-based renewable energy projects. Predicting carbon lost as a result of construction of wind farms built on peatland has not been fully characterised and this research will provide data that can supplement current 'carbon payback calculator' models for wind farms that aim to reinforce their 'green' credentials. Transfer of carbon from the terrestrial peatland systems to the aquatic freshwater and oceanic systems is most predominant during periods of high rainfall. It has been estimated that 50% of carbon is exported during only 10% of highest river flows, (Hinton et al., 1998). Furthermore, carbon export from peatlands is known to have a seasonal aspect with highest concentrations of dissolved organic carbon (DOC) found mostly in late summer months of August and September and lowest in December and January, (Dawson et al., 2004). Event sampling, where high intensity sample collection is carried out during high river flow periods, offers a better insight, understanding and estimation of carbon aquatic fluxes from peatland landscapes. The Gordonbush estate, near Brora, has an extensive peatland area where a wind farm development has recently been completed (April 2012). Investigations of aquatic carbon fluxes from this peatland system were started in July 2010, in conjunction with the start of construction of the 35-turbine wind farm, with a strong focus on event sampling. Fieldwork and sample collection is due to continue until at least September 2013 but data collated so far shows seasonal differences of carbon export from similar sized hydrological events. In addition, event sampling has highlighted the different characteristics between DOC and POC export as well as their contribution to the overall aquatic carbon flux. Phosphorous and nitrate concentrations have also been analysed and their export regimes and interactions with carbon export will also be discussed.

  13. Why freshwater organisms survived the asteroid that killed the dinosaurs

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2013-08-01

    Roughly 65.5 million years ago, a massive asteroid smashed into present-day Chicxulub, Mexico. The impact set fire to Earth's surface. Dust and ash darkened the sky, sending the planet into an "impact winter" that lasted months to years and caused the extinction of nonavian dinosaurs and half of ocean-dwelling species. However, life in inland freshwater ecosystems largely escaped this fate. To try to understand why freshwater organisms held on while ocean life failed, Robertson et al. surveyed relevant research to understand how the mechanisms of extinction would have operated differently in the two environments.

  14. Ocean nutrients

    NASA Astrophysics Data System (ADS)

    Boyd, Philip W.; Hurd, Catriona L.

    Nutrients provide the chemical life-support system for phytoplankton in the ocean. Together with the carbon fixed during photosynthesis, nutrients provide the other elements, such as N and P, needed to synthesize macromolecules to build cellular constituents such as ribosomes. The makeup of these various biochemicals, such as proteins, pigments, and nucleic acids, together determine the elemental stoichiometry of an individual phytoplankton cell. The stoichiometry of different phytoplankton species or groups will vary depending on the proportions of distinct cellular machinery, such as for growth or resource acquisition, they require for their life strategies. The uptake of nutrients by phytoplankton helps to set the primary productivity, and drives the biological pump, of the global ocean. In the case of nitrogen, the supply of nutrients is categorized as either new or regenerated. The supply of new nitrogen, such as nitrate upwelled from the ocean' interior or biological nitrogen fixation, is equal to the vertical export of particular organic matter from the upper ocean on a timescale of years. Nutrients such as silica can also play a structural role in some phytoplankton groups, such as diatoms, where they are used to synthesize a siliceous frustule that offers some mechanical protection from grazers. In this chapter, we also explore nutrient uptake kinetics, patterns in nutrient distributions in space and time, the biogeochemical cycle of nitrogen, the atmospheric supply of nutrients, departures from the Redfield ratio, and whether nutrient distributions and cycling will be altered in the future

  15. Methanotrophy controls groundwater methane export from a barrier island

    NASA Astrophysics Data System (ADS)

    Schutte, Charles A.; Wilson, Alicia M.; Evans, Tyler; Moore, Willard S.; Joye, Samantha B.

    2016-04-01

    Methane concentrations can be high in coastal groundwater, resulting in methane export driven by submarine groundwater discharge. However, the magnitude of this methane flux depends significantly on the rate of methanotrophy, the often overlooked process of microbial methane consumption that occurs within coastal aquifer sediments. Here we describe a zone of methanogenesis within the freshwater lens of a barrier island aquifer and investigate the methane source/sink behavior of the barrier island system as a whole. The median concentration of methane dissolved in fresh groundwater beneath the center of the island was 0.6 mM, supported by high rates of potential methanogenesis (22 mmol m-2 day-1). However, rates of microbial methane consumption were also elevated in surrounding sediments (18 mmol m-2 day-1). Groundwater flowing from the zone of methanogenesis to the point of discharge into the ocean had a long residence time within methanotrophic sediments (∼195 days) such that the majority of the methane produced within the barrier island aquifer was likely consumed there.

  16. The freshwater biodiversity crisis.

    PubMed

    Brautigam, A

    1999-01-01

    This article concerns the threat on freshwater ecosystems, which harbor a disproportionate amount of the world's biodiversity. In many parts of the world, freshwater ecosystems are already degraded from a range of human activities, including water extraction, pollution and physical alteration. The data that showed a biodiversity crisis in ecosystems included species loss and breakdown of the ecological processes and resources. Furthermore, several case studies were cited to illustrate the status of freshwater diversity. Numerous reasons for freshwater biodiversity loss were mentioned, which included pollution from pesticides and agricultural and mine run-off, and physical alteration through channelization and impoundments that affected the hydrology and benthic habitat. Despite the successful establishment of institutions to conserve water birds and wetland habitats, there was a lower priority for conservation of freshwater biodiversity in terms of species and habitats. This bias has had important and serious implications for allocation of resources to increase the knowledge and understanding of freshwater ecosystems, as well as for the adequacy of impact assessments for development projects affecting them. PMID:12349584

  17. Evidence of local short-distance spawning migration of tropical freshwater eels, and implications for the evolution of freshwater eel migration

    PubMed Central

    Arai, Takaomi

    2014-01-01

    Freshwater eels have fascinated biologists for centuries due to the spectacular long-distance migrations between the eels’ freshwater habitats and their spawning areas far out in the ocean and the mysteries of their ecology. The spawning areas of Atlantic eels and Japanese eel were located far offshore in the Atlantic Ocean and the Pacific Ocean, respectively, and their reproduction took place thousands of kilometers away from their growth habitats. Phylogenetic studies have revealed that freshwater eels originated in the Indonesian region. However, remarkably little is known about the life histories of tropical freshwater eels despite the fact that tropical eels are key to understanding the nature of primitive forms of catadromous migration. This study found spawning-condition tropical freshwater eels in Lake Poso, central Sulawesi, Indonesia, with considerably high gonadosomatic index values and with histologically fully developed gonads. This study provides the first evidence that under certain conditions, freshwater eels have conditions that are immediately able to spawn even in river downstream. The results suggest that, in contrast to the migrations made by the Atlantic and Japanese eels, freshwater eels originally migrated only short distances of <100 kilometers to local spawning areas adjacent to their freshwater growth habitats. Ancestral eels most likely underwent a catadromous migration from local short-distance movements in tropical coastal waters to the long-distance migrations characteristic of present-day temperate eels, which has been well established as occurring in subtropical gyres in both hemispheres. PMID:25614795

  18. Fluxes of Colloidal Organic Carbon to the Arctic Ocean From North American Rivers

    NASA Astrophysics Data System (ADS)

    Cai, Y.; Guo, L.

    2005-12-01

    Colloidal organic carbon (COC) is a major component in the carbon biogeochemical cycle. The Arctic Ocean receives a disproportionally large input of global terrestrial organic carbon, but the riverine input of COC to the Arctic Ocean is still poorly quantified. Water samples were collected during Summer 2005 from the Mackenzie River, Sagavanirktok River, Kuparuk River, and the Yukon River Basin, including Yukon River, Tanana River and Chena River. Using cross-flow ultrafiltration, the concentration of COC (1kD to 0.45um) and its percentage in bulk dissolved organic carbon (DOC) were quantified with the application of an ultrafiltration permeation model. Riverine export fluxes of COC by these rivers were also estimated based on freshwater discharge and corresponding COC concentrations. COC concentrations derived from the ultrafiltration permeation model ranged from 0.54 to 14.3 mg-C/L, while the percentages of COC in the bulk DOC remained somewhat constant, ranging from 62 to 77% with an average of 68+/-5%. These COC percentages are higher than those found in tropical/subtropical rivers, indicating the importance of COC in the Arctic rivers. The annual export flux of COC was 2.30E+12 g-C/y for the Yukon River, 1.23x1012 g-C/y for the Mackenzie River, 1.51x109 g-C/y for the Sagavanirktok River, and 3.89x109 g-C/y for the Kuparuk River. Within the COC export flux from the Yukon River Basin, ~65% was from the Yukon River, ~3% was from the Tanana River, and 32% was from the Koyukuk River and other tributaries. The total COC discharged by rivers into the Arctic Ocean was estimated as 12.2-17.7x1012 g-C/y, given a DOC flux of 18-26x1012 g-C/y to the Arctic Ocean and an average COC percentage of 68%.

  19. Information to help reduce environmental impacts from freshwater oil spills

    SciTech Connect

    Fritz, D.E.; Steen, A.E.

    1995-12-31

    The American Petroleum Institute (API) has been working since 1990 to provide information to help the response community minimize the impact of spills to pared jointly with the US inland freshwater. Projects have included a manual, pre National Oceanic and Atmospheric Administration (NOAA), to give guidance on the cleanup techniques that will minimize environmental impacts on spills in freshwater habitats. Nearing completion are a literature review and annotated bibliography of the environmental and human health effects of oil spilled in freshwater habitats. The use of chemical treating agents for freshwater spill applications is being studied with input from other industry and government groups. A project has begun, with funding from API, the Louisiana Applied Oil Spill Research and Development Program, NOAA, the Marine Spill Response Corporation (MSRC), and the US Department of Energy, to evaluate in situ burning of oil spilled in marshes.

  20. Observing the Arctic Ocean under melting ice - the UNDER-ICE project

    NASA Astrophysics Data System (ADS)

    Sagen, Hanne; Ullgren, Jenny; Geyer, Florian; Bergh, Jon; Hamre, Torill; Sandven, Stein; Beszczynska-Mller, Agnieszka; Falck, Eva; Gammelsrd, Tor; Worcester, Peter

    2014-05-01

    The sea ice cover of the Arctic Ocean is gradually diminishing in area and thickness. The variability of the ice cover is determined by heat exchange with both the atmosphere and the ocean. A cold water layer with a strong salinity gradient insulates the sea ice from below, preventing direct contact with the underlying warm Atlantic water. Changes in water column stratification might therefore lead to faster erosion of the ice. As the ice recedes, larger areas of surface water are open to wind mixing; the effect this might have on the water column structure is not yet clear. The heat content in the Arctic strongly depends on heat transport from other oceans. The Fram Strait is a crucial pathway for the exchange between the Arctic and the Atlantic Ocean. Two processes of importance for the Arctic heat and freshwater budget and the Atlantic meridional overturning circulation take place here: poleward heat transport by the West Spitzbergen Current and freshwater export by the East Greenland Current. A new project, Arctic Ocean under Melting Ice (UNDER-ICE), aims to improve our understanding of the ocean circulation, water mass distribution, fluxes, and mixing processes, sea ice processes, and net community primary production in ice-covered areas and the marginal ice zone in the Fram Strait and northward towards the Gakkel Ridge. The interdisciplinary project brings together ocean acoustics, physical oceanography, marine biology, and sea ice research. A new programme of observations, integrated with satellite data and state-of-the-art numerical models, will be started in order to improve the estimates of heat, mass, and freshwater transport between the North Atlantic and the Arctic Ocean. On this poster we present the UNDER-ICE project, funded by the Research Council of Norway and GDF Suez E&P Norge AS for the years 2014-2017, and place it in context of the legacy of earlier projects in the area, such as ACOBAR. A mooring array for acoustic tomography combined with "standard" oceanographic measurements of current velocity and water mass properties will be deployed in the Fram Strait in September 2014. The dynamic processes in the marginal ice zone, in particular internal waves, mesoscale eddies, and front instabilities, will be explored using model experiments and high temporal resolution measurements. The results of the observational data analysis and model simulations will be integrated and compared with global climate model simulations (CMIP5). Satellite-derived data products will also be included in the synthesis. As part of the UNDER-ICE project, a web portal for Arctic data will be developed, that will offer open access to metadata and observational and model data products to support studies of Arctic climate and climate change.

  1. Vectors of invasions in freshwater invertebrates and fishes

    USGS Publications Warehouse

    Fuller, Pam L.

    2015-01-01

    Without human assistance, the terrestrial environment and oceans represent barriers to the dispersal of freshwater aquatic organisms. The ability to overcome such barriers depends on the existence of anthropogenic vectors that can transport live organisms to new areas, and the species biology to survive the transportation and transplantation into the new environment (Johnson etal., 2006).

  2. Freshwater Education: The Need, The Tools, and The "Vital Link."

    ERIC Educational Resources Information Center

    Shroeder, Linda

    1984-01-01

    Freshwater education programs are beginning to instill in young people a sense of awareness and a sense of responsibility regarding the future of water resources. Several of these programs are discussed, including Project COAST (Coastal, Oceanic, and Aquatic Studies) and "Acid Precipitation Learning Materials, Grades 7-12." (JN)

  3. Multimodel simulations of Arctic Ocean sea surface height variability in the period 1970-2009

    NASA Astrophysics Data System (ADS)

    Koldunov, Nikolay V.; Serra, Nuno; Khl, Armin; Stammer, Detlef; Henry, Olivier; Cazenave, Anny; Prandi, Pierre; Knudsen, Per; Andersen, Ole Baltazar; Gao, Yongqi; Johannessen, Johnny

    2014-12-01

    The performance of several numerical ocean models is assessed with respect to their simulation of sea surface height (SSH) in the Arctic Ocean, and the main patterns of SSH variability and their causes over the past 40 years (1970-2009) are analyzed. In comparison to observations, all tested models broadly reproduce the mean SSH in the Arctic and reveal a good correlation with both tide gauge data and SSH anomalies derived from satellite observations. Although the models do not represent the positive Arctic SSH trend observed over the last two decades, their interannual-to-decadal SSH variability is in reasonable agreement with available measurements. Focusing on results from one of the models for a detailed analysis, it is shown that the decadal-scale SSH variability over shelf areas and deep parts of the Arctic Ocean have pronounced differences that are determined mostly by salinity variations. A further analysis of the three time periods 1987-1992, 1993-2002, and 2003-2009, corresponding to the transition times between cyclonic and anticyclonic regimes of the atmospheric circulation over the Arctic, revealed an unusual increase of SSH in the Amerasian basin during 2003-2009. Results from this model support the recent finding that the increase is caused mainly by changes in freshwater content brought about by the freshwater export through the Canadian Arctic Archiplago and increased Ekman pumping in the Amerasian basin and partly by lateral freshwater transport changes, leading to a redistribution of low-salinity shelf water. Overall, we show that present-day models can be used for investigating the reasons for low-frequency SSH variability in the region.

  4. Freshwater aspects of anadromous salmonid enhancement

    USGS Publications Warehouse

    Gould, Rowan W.

    1982-01-01

    Freshwater enhancement of anadromous salmonid populations has been practiced in the United States and Canada since the late 1800's. Reduction of natural spawning habitat and increasing fishing pressure make artificial enhancement a possible alternative to declining populations. Enhancement of anadromous salmonids involved improvement of the natural environment and reducing natural mortality. Methods of enhancement include fishways, spawning and rearing channels, stream rehabilitation, lake fertilization, environmental management, and artificial propagation techniques. Five Pacific salmon species and steelhead trout are commonly enhanced, primarily in watershed entering the Pacific Ocean and Great Lakes. Enhancement efforts contribute heavily to a commercial and sport industry realizing over $1.5 billion.

  5. ABC transporters: bacterial exporters.

    PubMed Central

    Fath, M J; Kolter, R

    1993-01-01

    The ABC transporters (also called traffic ATPases) make up a large superfamily of proteins which share a common function and a common ATP-binding domain. ABC transporters are classified into three major groups: bacterial importers (the periplasmic permeases), eukaryotic transporters, and bacterial exporters. We present a comprehensive review of the bacterial ABC exporter group, which currently includes over 40 systems. The bacterial ABC exporter systems are functionally subdivided on the basis of the type of substrate that each translocates. We describe three main groups: protein exporters, peptide exporters, and systems that transport nonprotein substrates. Prototype exporters from each group are described in detail to illustrate our current understanding of this protein family. The prototype systems include the alpha-hemolysin, colicin V, and capsular polysaccharide exporters from Escherichia coli, the protease exporter from Erwinia chrysanthemi, and the glucan exporters from Agrobacterium tumefaciens and Rhizobium meliloti. Phylogenetic analysis of the ATP-binding domains from 29 bacterial ABC exporters indicates that the bacterial ABC exporters can be divided into two primary branches. One branch contains the transport systems where the ATP-binding domain and the membrane-spanning domain are present on the same polypeptide, and the other branch contains the systems where these domains are found on separate polypeptides. Differences in substrate specificity do not correlate with evolutionary relatedness. A complete survey of the known and putative bacterial ABC exporters is included at the end of the review. PMID:8302219

  6. Freshwater runoff and salinity distribution in the Loxahatchee River estuary, southeastern Florida, 1980-82

    USGS Publications Warehouse

    Russell, G.M.; McPherson, B.F.

    1984-01-01

    Freshwater mixed with seawater over a distance of 5 to 10 river miles in the Loxahatchee River estuary during a recent study. Large freshwater inflows vertically stratified the estuary and shifted the mixing zone seaward. In the northwest fork of the estuary, the saltwater-freshwater interface moved daily about 0.5 to 1.5 river miles as a result of tides, and annually about 3 to 5 miles as a result of seasonal changes in freshwater inflow. In the southwest fork, saltwater movement upstream was blocked by a gate and dam structure in Canal-18, 4.7 miles upstream from the Atlantic Ocean. Although Canal-18 discharged about one-third of the total freshwater tributary inflow to the estuary, the effects of canal discharge on salinity were limited to relatively brief periods. Much of the time, no freshwater was discharged. (USGS)

  7. Freshwater runoff and salinity distribution in the Loxahatchee River estuary, southeastern Florida, 1980-1982

    SciTech Connect

    Russell, G.M.; McPherson, B.F.

    1984-01-01

    During a recent study, freshwater mixed with seawater over a distance of 5 to 10 river miles in the Loxahatchee River estuary. Large freshwater inflows vertically stratified the estuary and shifted the mixing zone seaward. In the northwest fork of the estuary, the saltwater-freshwater interface moved daily about 0.5 to 1.5 river miles as a result of tides and annually about 3 to 5 miles as a result of seasonal changes in freshwater inflow. In the southwest fork, saltwater movement upstream was blocked by a gate and dam structure in Canal-18, 4.7 miles upstream from the Atlantic Ocean. Although Canal-18 discharged about one-third of the total freshwater tributary inflow to the estuary, the effects of canal discharge on salinity were limited to relatively brief periods. Much of the time, no freshwater was discharged. 15 refs., 21 figs., 4 tabs.

  8. Model sensitivity of the Weddell and Ross seas, Antarctica, to vertical mixing and freshwater forcing

    NASA Astrophysics Data System (ADS)

    Kjellsson, Joakim; Holland, Paul R.; Marshall, Gareth J.; Mathiot, Pierre; Aksenov, Yevgeny; Coward, Andrew C.; Bacon, Sheldon; Megann, Alex P.; Ridley, Jeff

    2015-10-01

    We examine the sensitivity of the Weddell and Ross seas to vertical mixing and surface freshwater forcing using an ocean-sea ice model. The high latitude Southern Ocean is very weakly stratified, with a winter salinity difference across the pycnocline of only ?0.2 PSU. We find that insufficient vertical mixing, freshwater supply from the Antarctic Ice Sheet, or initial sea ice causes a high salinity bias in the mixed layer which erodes the stratification and causes excessive deep convection. This leads to vertical homogenisation of the Weddell and Ross seas, opening of polynyas in the sea ice and unrealistic spin-up of the subpolar gyres and Antarctic Circumpolar Current. The model freshwater budget shows that a ?30% error in any component can destratify the ocean in about a decade. We find that freshwater forcing in the model should be sufficient along the Antarctic coastline to balance a salinity bias caused by dense coastal water that is unable to sink to the deep ocean. We also show that a low initial sea ice area introduces a salinity bias in the marginal ice zone. We demonstrate that vertical mixing, freshwater forcing and initial sea ice conditions need to be constrained simultaneously to reproduce the Southern Ocean hydrography, circulation and sea ice in a model. As an example, insufficient vertical mixing will cause excessive convection in the Weddell and Ross seas even in the presence of large surface freshwater forcing and initial sea ice cover.

  9. 77 FR 12583 - Ocean Transportation Intermediary License; Applicants

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-03-01

    ... Ocean Transportation Intermediary License; Applicants Notice is hereby given that the following...-Operating Common Carrier (NVO) and/or Ocean Freight Forwarder (OFF)--Ocean Transportation Intermediary (OTI..., Dulles, VA 20166, Officers: Philippe Pierson, Vice President of Ocean Exports (Qualifying...

  10. On multiple equilibria of the global ocean circulation and the preference for North Atlantic sinking

    NASA Astrophysics Data System (ADS)

    Huisman, S. E.

    2010-12-01

    In the ocean circulation there is the peculiar feature that heat transport is northwards throughout the entire Atlantic ocean. This means that the Atlantic heat transport in the southern hemisphere is towards the equator. Also, the heat transport in the Atlantic is much larger that in the Pacific. This northward heat transport is mainly due to the meridional overturning circulation in the Atlantic, where surface waters flow northward, release their heat to the atmosphere (thus becoming colder and gaining density), sink to depth at high northern latitudes and flow southwards as so-called North Atlantic Deep Water. The question why there is deep water formation in the Atlantic ocean and not in the Pacific ocean is central to this thesis. Deep water formation, or the sinking of water, is possible, because the water in the North Atlantic has high density. This high density is due to cold temperatures and high salt content, which is transported there by the surface currents. If the sinking is disrupted for some reason -- for example, melting of the Greenland ice sheet is very strong for a certain period, making the water of the North Atlantic too fresh to sink -- then the supply of salty water ceases too. This means the sinking of the water cannot just begin again; the water is too buoyant. The boundary conditions have not changed (the melt has stabilized at the former rate, there are no changes in precipitation and atmospheric temperature), but still the ocean circulation is fundamentally different from before. This notion, that there are multiple possible circulation patterns under equal forcing, is called the concept of multiple equilibria. There is more and more paleoclimatic evidence that such a collapse of the meridional overturning circulation has happened in the past sometimes, for example at the end of the last glacial. In this thesis I argue that these multiple equilibria are important to explain the salinity contrast and the difference in meridional flow between the Atlantic and Pacific. The main argument is that there is a certain selection process, that starts deep water formation at a certain location. Then the salt transport by the currents will help to sustain the meridional overturning circulation that arises. I also turn to the question how we could measure whether or not the ocean circulation is close to a collapse. The idea is that if the overturning circulation imports freshwater (at the boundary at 35 Southern Latitude, and it slows down for some reason, then the import of freshwater slows down too, thereby making the North Atlantic saltier again and increasing the sinking motion. However, when the meridional overturning circulation exports freshwater and it slows down for some reason, then there will be accumulation of freshwater, decreasing the density and slowing the sinking motion even more. So, if we can determine whether the overturning circulation imports or exports freshwater, we also have determined if it can potentially collapse.

  11. A New Look at the Arctic Freshwater Cycle: The Charge of the Budgeteers

    NASA Astrophysics Data System (ADS)

    Serreze, M. C.

    2005-12-01

    The Budgeteers, a working group within the NSF-ARCSS Freshwater Initiative, seeks to quantify and link the major terms of the large-scale freshwater cycle of the Arctic. Working group members and contributing colleagues from the University of Colorado (M. Serreze, A. Barrett, A. Slater), the University of Washington (R. Woodgate, K. Aagaard, M. Steele, R. Moritz, C. Lee), the University of New Hampshire (R. Lammers, C. Vorosmarty) and the British Antarctic Survey (M. Meredith) bring varied expertise in the atmospheric, oceanic and land surface components of the Arctic system. We draw from recent oceanographic observations, land surface and hydrologic models, and results from the ECMWF ERA-40 reanalysis. Despite large uncertainties in some of the terms, particularly the oceanic fluxes of liquid water through Fram Strait and the complex channels of the Canadian Arctic Archipelago (for which data are very limited), the mean annual freshwater budget of the combined atmosphere, land and ocean system is reasonably well closed. Outputs exceed inputs by 791 cubic km. However, this imbalance is only about 10 percent of the estimated annual freshwater input to the Arctic Ocean which is driven primarily by river runoff, precipitation less evapo-transpiration (P-ET) over the Arctic Ocean, and the flow of low-salinity waters into the Arctic Ocean through Bering Strait. Terms for which records are sufficient for more focused analysis show strong seasonal and interannual variability. Seasonality in combined runoff, P-ET over the Arctic Ocean, Bering Strait inflow and the Fram Strait ice flux contribute, along with variations in sea ice, to a spring to summer increase in oceanic freshwater storage. The Fram Strait ice outflow shows the largest interannual variability. We estimate a mean residence time of freshwater in the Arctic Ocean of approximately nine years, contrasting sharply with the atmosphere, with a residence time of about seven days.

  12. Multiyear Survey of the Distribution and Fate of Biomarkers in the Atlantic Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Fietz, S.; Rosell Mele, A.; Rueda, G.; Martinez Garcia, A.; Hambach, B.; Viladrich, N.; Barrera Sansn, A.; Rossi, S.; Ziveri, P.

    2010-12-01

    Biogeochemical signatures derived from organisms thriving in the ocean water column are driven by environmental conditions, with highly complex processes linking primary and export productivity. Organic matter input, in-situ production and fate depend on conditions such as sea surface temperature, ice-cover and freshwater input, mixing/stratification regime, fertilization and acidification etc. for which important changes are predicted in subpolar and polar environments. However, the spatial and interannual variability of organic matter distribution and their driving environmental factors in these vast oceanic regions are not fully determined or understood. To gain some new insights into these issues in the Arctic region we have participated in a multiyear survey, based on four summer cruises from 2005 to 2009 following latitudinal transects from the North Atlantic to the Fram Strait, and longitudinal transects from Greenland to Svalbard and collected particulate matter in the water column as well as twenty surface sediments. We focus on biogeochemical markers for terrestrial matter input (e.g., n-alkanes, branched GDGTs), for in-situ productivity and pelagic community composition (e.g., photosynthetic pigments, alkenones, isoprenoid GDGTs) and food-web structure (e.g., fatty acids, sterols). We also collected samples to determine the distribution of specific algal groups (coccolithophores) in this region. Results from the 2008 and 2009 surveys will be presented. Our aim is to compare the organic matter signatures in the upper water column to those in the exported matter that reaches deep water masses and surface sediments.

  13. Anticipated Improvements to Net Surface Freshwater Fluxes from GPM

    NASA Technical Reports Server (NTRS)

    Smith, Eric A.

    2005-01-01

    Evaporation and precipitation over the oceans play very important roles in the global water cycle, upper-ocean heat budget, ocean dynamics, and coupled ocean-atmosphere dynamics. In the conventional representation of the terrestrial water cycle, the assumed role of the oceans is to act as near-infinite reservoirs of water with the main drivers of the water cycle being land- atmosphere interactions in which excess precipitation (P) over evaporation (E) is returned to the oceans as surface runoff and baseflow. Whereas this perspective is valid for short space and time scales -- fundamental principles, available observed estimates, and results from models indicate that the oceans play a far more important role in the large-scale water cycle at seasonal and longer timescales. Approximately 70-80% of the total global evaporation and precipitation occurs over oceans. Moreover, latent heat release into the atmosphere over the oceans is the major heat source driving global atmospheric circulations, with the moisture transported by circulations from oceans to continents being the major source of water precipitating over land. Notably, the major impediment in understanding and modeling the oceans role in the global water cycle is the lack of reliable net surface freshwater flux estimates (E - P fluxes) at the salient spatial and temporal resolutions, i.e., consistent coupled weekly to monthly E - P gridded datasets.

  14. Acidification of freshwaters

    SciTech Connect

    Cresser, M.S.; Edwards, A.C.

    1987-01-01

    This volume gives an account that draws not only on the main branches of chemistry but also on soil physics, chemistry, hydrology, meteorology, geography, geology, plant physiology, soil microbiology and zoology. The author examine the numerous interacting physical, chemical, and biological, processes that regulate the acidity of freshwaters, a phenomenon that has various causes, including precipitation; acidifying pollutions; and the interaction of plants, soils and water. The relative importance of the different processes is examined.

  15. Estimating freshwater flows from tidally affected hydrographic data

    NASA Astrophysics Data System (ADS)

    Pagendam, D. E.; Percival, D. B.

    2015-03-01

    Detiding end-of-catchment flow data are an important step in determining the total volumes of freshwater (and associated pollutant loads) entering the ocean. We examine three approaches for separating freshwater and tidal flows from tidally affected data: (i) a simple low-pass Butterworth filter (BWF); (ii) a robust, harmonic analysis with Kalman smoothing (RoHAKS) which is a novel approach introduced in this paper; and (iii) dynamic harmonic regression (DHR). Using hydrographic data collected in the Logan River, Australia, over a period of 452 days, we judge the accuracy of the three methods based on three criteria: consistency of freshwater flows with upstream gauges; consistency of total discharge volumes with the raw data over the event; and minimal upstream flow. A simulation experiment shows that RoHAKS outperforms both BWF and DHR on a number of criteria. In addition, RoHAKS enjoys a computational advantage over DHR in speed and use of freely available software.

  16. Effects of pollution on freshwater organisms

    SciTech Connect

    Phipps, G.L.; Harden, M.J.; Leonard, E.N.; Roush, T.H; Spehar, D.L.; Stephan, C.E.; Pickering, Q.H.; Buikema, A.L. Jr.

    1984-06-01

    This review includes subjects in last year's reviews on effects of pollution on freshwater invertebrates and effects of pollution on freshwater fish and amphibians. This review also includes information on the effects of pollution on freshwater plants. 625 references.

  17. Ocean Observations of Climate Change

    NASA Astrophysics Data System (ADS)

    Chambers, Don

    2016-01-01

    The ocean influences climate by storing and transporting large amounts of heat, freshwater, and carbon, and exchanging these properties with the atmosphere. About 93% of the excess heat energy stored by the earth over the last 50 years is found in the ocean. More than three quarters of the total exchange of water between the atmosphere and the earth's surface through evaporation and precipitation takes place over the oceans. The ocean contains 50 times more carbon than the atmosphere and is at present acting to slow the rate of climate change by absorbing one quarter of human emissions of carbon dioxide from fossil fuel burning, cement production, deforestation and other land use change.Here I summarize the observational evidence of change in the ocean, with an emphasis on basin- and global-scale changes relevant to climate. These include: changes in subsurface ocean temperature and heat content, evidence for regional changes in ocean salinity and their link to changes in evaporation and precipitation over the oceans, evidence of variability and change of ocean current patterns relevant to climate, observations of sea level change and predictions over the next century, and biogeochemical changes in the ocean, including ocean acidification.

  18. Carbon export by small particles in the Norwegian Sea

    NASA Astrophysics Data System (ADS)

    Dall'Olmo, Giorgio; Mork, Kjell Arne

    2014-04-01

    Despite its fundamental role in controlling the Earth's climate, present estimates of global organic carbon export to the deep sea are affected by relatively large uncertainties. These uncertainties are due to lack of observations as well as disagreement among methods and assumptions used to estimate carbon export. Complementary observations are thus needed to reduce these uncertainties. Here we show that optical backscattering measured by Bio-Argo floats can detect a seasonal carbon export flux in the Norwegian Sea. This export was most likely due to small particles (i.e., 0.2-20 ?m), was comparable to published export values, and contributed to long-term carbon sequestration. Our findings highlight the importance of small particles and of physical mixing in the biological carbon pump and support the use of autonomous platforms as tools to improve our mechanistic understanding of the ocean carbon cycle.

  19. Management of freshwater lenses on small Pacific islands

    NASA Astrophysics Data System (ADS)

    White, Ian; Falkland, Tony

    2010-02-01

    The nature of shallow aquifers and the impacts of seawater intrusion in small islands within the Pacific Ocean are reviewed. Many Pacific islands rely on shallow fresh groundwater lenses in highly permeable aquifers, underlain and surrounded by seawater, as their principal freshwater source. It is argued here that, in small islands, the nature of fresh groundwater lenses and their host aquifers coupled with frequent natural and ever-present anthropogenic threats make them some of the most vulnerable aquifer systems in the world. A simple steady-state approximation is used to provide insight into the key climatic, hydrogeological, physiographic, and management factors that influence the quantity of, and saline intrusion into freshwater lenses. Examples of the dynamic nature of freshwater lenses as they respond to these drivers are given. Natural and human-related threats to freshwater lenses are discussed. Long dry periods strongly coupled to sea surface temperatures impact on the quantity and salinity of fresh groundwater. The vulnerability of small island freshwater lenses dictates careful assessment, vigilant monitoring, appropriate development, and astute management. Strategies to aid future groundwater sustainability in small islands are presented and suggested improvements to donor and aid programs in water are also advanced.

  20. JPL Export Compliance Program

    NASA Technical Reports Server (NTRS)

    Momjian, E.; Lam, C.

    2000-01-01

    The transfer of commodities, software, or technlogies to foreign persons is subject to U.S. export control laws and regulations. These export controls are applicable, regardless of whether the transfer occurs in the U.S. or outside of the U.S.

  1. Sperm in "parhenogenetic" freshwater gastrotrichs.

    PubMed

    Weiss, M J; Levy, D P

    1979-07-20

    Freshwater members of the phylum Gastrotricha have been considered obligate parthenogens. In Lepidodermelia squammata, the species for which there is most evidence for parthenogenesis, sperm have been discovered. This finding will necessitate reexamination of the nature of sexuality and life cycles and of the concept of "species" in freshwater gastrotrichs. PMID:17747043

  2. Hosed vs. unhosed: global response to interruptions of the Atlantic Meridional Overturning, with and without freshwater forcing

    NASA Astrophysics Data System (ADS)

    Brown, N.; Galbraith, E. D.

    2015-10-01

    It is well known that glacial periods were punctuated by abrupt climate changes, with large impacts on air temperature, precipitation, and ocean circulation across the globe. However, the long-held idea that freshwater forcing, caused by massive iceberg discharges, was the driving force behind these changes has been questioned in recent years. This throws into doubt the abundant literature on modelling abrupt climate change through "hosing" experiments, whereby the Atlantic Meridional Overturning Circulation (AMOC) is interrupted by an injection of freshwater to the North Atlantic: if some, or all, abrupt climate change was not driven by freshwater input, could its character have been very different than the typical hosed experiments? Here, we take advantage of a global coupled ocean-atmosphere model that exhibits spontaneous, unhosed oscillations in AMOC strength, in order to examine how the global imprint of AMOC variations depends on whether or not it is the result of external freshwater input. The results imply that, to first order, the ocean-ice-atmosphere dynamics associated with an AMOC weakening dominate the global response, regardless of whether or not freshwater input is the cause. The exception lies in the impact freshwater inputs can have on the strength of other polar haloclines, particularly the Southern Ocean, to which freshwater can be transported relatively quickly after injection in the North Atlantic.

  3. Analysis of the Arctic system for freshwater cycle intensification: Observations and expectations

    USGS Publications Warehouse

    Rawlins, M.A.; Steele, M.; Holland, M.M.; Adam, J.C.; Cherry, J.E.; Francis, J.A.; Groisman, P.Y.; Hinzman, L.D.; Huntington, T.G.; Kane, D.L.; Kimball, J.S.; Kwok, R.; Lammers, R.B.; Lee, C.M.; Lettenmaier, D.P.; McDonald, K.C.; Podest, E.; Pundsack, J.W.; Rudels, B.; Serreze, M.C.; Shiklomanov, A.; Skagseth, O.; Troy, T.J.; Vorosmarty, C.J.; Wensnahan, M.; Wood, E.F.; Woodgate, R.; Yang, D.; Zhang, K.; Zhang, T.

    2010-01-01

    Hydrologic cycle intensification is an expected manifestation of a warming climate. Although positive trends in several global average quantities have been reported, no previous studies have documented broad intensification across elements of the Arctic freshwater cycle (FWC). In this study, the authors examine the character and quantitative significance of changes in annual precipitation, evapotranspiration, and river discharge across the terrestrial pan-Arctic over the past several decades from observations and a suite of coupled general circulation models (GCMs). Trends in freshwater flux and storage derived from observations across the Arctic Ocean and surrounding seas are also described. With few exceptions, precipitation, evapotranspiration, and river discharge fluxes from observations and the GCMs exhibit positive trends. Significant positive trends above the 90% confidence level, however, are not present for all of the observations. Greater confidence in the GCM trends arises through lower interannual variability relative to trend magnitude. Put another way, intrinsic variability in the observations tends to limit confidence in trend robustness. Ocean fluxes are less certain, primarily because of the lack of long-term observations. Where available, salinity and volume flux data suggest some decrease in saltwater inflow to the Barents Sea (i.e., a decrease in freshwater outflow) in recent decades. A decline in freshwater storage across the central Arctic Ocean and suggestions that large-scale circulation plays a dominant role in freshwater trends raise questions as to whether Arctic Ocean freshwater flows are intensifying. Although oceanic fluxes of freshwater are highly variable and consistent trends are difficult to verify, the other components of the Arctic FWC do show consistent positive trends over recent decades. The broad-scale increases provide evidence that the Arctic FWC is experiencing intensification. Efforts that aim to develop an adequate observation system are needed to reduce uncertainties and to detect and document ongoing changes in all system components for further evidence of Arctic FWC intensification.

  4. Landscape scale controls on the vascular plant component of dissolved organic carbon across a freshwater delta

    USGS Publications Warehouse

    Eckard, Robert S.; Hernes, Peter J.; Bergamaschi, Brian A.; Stepanauskas, Ramunas; Kendall, Carol

    2007-01-01

    Lignin phenol concentrations and compositions were determined on dissolved organic carbon (DOC) extracts (XAD resins) within the Sacramento-San Joaquin River Delta (the Delta), the tidal freshwater portion of the San Francisco Bay Estuary, located in central California, USA. Fourteen stations were sampled, including the following habitats and land-use types: wetland, riverine, channelized waterway, open water, and island drains. Stations were sampled approximately seasonally from December, 1999 through May, 2001. DOC concentrations ranged from 1.3 mg L-1 within the Sacramento River to 39.9 mg L-1 at the outfall from an island drain (median 3.0 mg L-1), while lignin concentrations ranged from 3.0 ?L-1 within the Sacramento River to 111 ?L-1 at the outfall from an island drain (median 11.6 ?L-1). Both DOC and lignin concentrations varied significantly among habitat/land-use types and among sampling stations. Carbon-normalized lignin yields ranged from 0.07 mg (100 mg OC)-1 at an island drain to 0.84 mg (100 mg OC)-1 for a wetland (median 0.36 mg (100 mg OC)-1), and also varied significantly among habitat/land-use types. A simple mass balance model indicated that the Delta acted as a source of lignin during late autumn through spring (10-83% increase) and a sink for lignin during summer and autumn (13-39% decrease). Endmember mixing models using S:V and C:V signatures of landscape scale features indicated strong temporal variation in sources of DOC export from the Delta, with riverine source signatures responsible for 50% of DOC in summer and winter, wetland signatures responsible for 40% of DOC in summer, winter, and late autumn, and island drains responsible for 40% of exported DOC in late autumn. A significant negative correlation was observed between carbon-normalized lignin yields and DOC bioavailability in two of the 14 sampling stations. This study is, to our knowledge, the first to describe organic vascular plant DOC sources at the level of localized landscape features, and is also the first to indicate a significant negative correlation between lignin and DOC bioavailability within environmental samples. Based upon observed trends: (1) Delta features exhibit significant spatial variability in organic chemical composition, and (2) localized Delta features appear to exert strong controls on terrigenous DOC as it passes through the Delta and is exported into the Pacific Ocean.

  5. Mechanisms governing interannual variability in upper-ocean inorganic carbon system and air-sea CO 2 fluxes: Physical climate and atmospheric dust

    NASA Astrophysics Data System (ADS)

    Doney, Scott C.; Lima, Ivan; Feely, Richard A.; Glover, David M.; Lindsay, Keith; Mahowald, Natalie; Moore, J. Keith; Wanninkhof, Rik

    2009-04-01

    We quantify the mechanisms governing interannual variability in the global, upper-ocean inorganic carbon system using a hindcast simulation (1979-2004) of an ecosystem-biogeochemistry model forced with time-evolving atmospheric physics and dust deposition. We analyze the variability of three key, interrelated metricsair-sea CO 2 flux, surface-water carbon dioxide partial pressure pCO 2, and upper-ocean dissolved inorganic carbon (DIC) inventorypresenting for each metric global spatial maps of the root mean square (rms) of anomalies from a model monthly climatology. The contribution of specific driving factors is diagnosed using Taylor expansions and linear regression analysis. The major regions of variability occur in the Southern Ocean, tropical Indo-Pacific, and Northern Hemisphere temperate and subpolar latitudes. Ocean circulation is the dominant factor driving variability over most of the ocean, modulating surface dissolved inorganic carbon that in turn alters surface-water pCO 2 and air-sea CO 2 flux variability (global integrated anomaly rms of 0.34 Pg C yr -1). Biological export and thermal solubility effects partially damp circulation-driven pCO 2 variability in the tropics, while in the subtropics, thermal solubility contributes positively to surface-water pCO 2 and air-sea CO 2 flux variability. Gas transfer and net freshwater inputs induce variability in the air-sea CO 2 flux in some specific regions. A component of air-sea CO 2 flux variability (global integrated anomaly rms of 0.14 Pg C yr -1) arises from variations in biological export production induced by variations in atmospheric iron deposition downwind of dust source regions. Beginning in the mid-1990s, reduced global dust deposition generates increased air-sea CO 2 outgassing in the Southern Ocean, consistent with trends derived from atmospheric CO 2 inversions.

  6. Modeling ocean circulation and biogeochemical variability in the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Xue, Z.; He, R.; Fennel, K.; Cai, W.-J.; Lohrenz, S.; Hopkinson, C.

    2013-05-01

    A three-dimensional coupled physical-biogeochemical model is applied to simulate and examine temporal and spatial variability of circulation and biogeochemical cycling in the Gulf of Mexico (GoM). The model is driven by realistic atmospheric forcing, open boundary conditions from a data assimilative global ocean circulation model, and observed freshwater and terrestrial nutrient input from major rivers. A 7 yr model hindcast (2004-2010) was performed, and validated against satellite observed sea surface height, surface chlorophyll, and in-situ observations including coastal sea-level, ocean temperature, salinity, and nutrient concentration. The model hindcast revealed clear seasonality in nutrient, phytoplankton and zooplankton distributions in the GoM. An Empirical Orthogonal Function analysis indicated a phase-locked pattern among nutrient, phytoplankton and zooplankton concentrations. The GoM shelf nutrient budget was also quantified, revealing that on an annual basis ~80% of nutrient input was denitrified on the shelf and ~17% was exported to the deep ocean.

  7. Modeling ocean circulation and biogeochemical variability in the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Xue, Z.; He, R.; Fennel, K.; Cai, W.-J.; Lohrenz, S.; Hopkinson, C.

    2013-11-01

    A three-dimensional coupled physical-biogeochemical model is applied to simulate and examine temporal and spatial variability of circulation and biogeochemical cycling in the Gulf of Mexico (GoM). The model is driven by realistic atmospheric forcing, open boundary conditions from a data assimilative global ocean circulation model, and observed freshwater and terrestrial nitrogen input from major rivers. A 7 yr model hindcast (2004-2010) was performed, and validated against satellite observed sea surface height, surface chlorophyll, and in situ observations including coastal sea level, ocean temperature, salinity, and dissolved inorganic nitrogen (DIN) concentration. The model hindcast revealed clear seasonality in DIN, phytoplankton and zooplankton distributions in the GoM. An empirical orthogonal function analysis indicated a phase-locked pattern among DIN, phytoplankton and zooplankton concentrations. The GoM shelf nitrogen budget was also quantified, revealing that on an annual basis the DIN input is largely balanced by the removal through denitrification (an equivalent of ~ 80% of DIN input) and offshore exports to the deep ocean (an equivalent of ~ 17% of DIN input).

  8. Potential Impacts of Food Production on Freshwater Availability

    NASA Astrophysics Data System (ADS)

    Yano, Shinjiro; Hanasaki, Naota; Itsubo, Norihiro; Kim, Hyungjun; Oki, Taikan

    2014-05-01

    The sustainability of freshwater use is often evaluated based on the total volume of water consumption or withdrawal. However, the renewable freshwater resource and potential impacts of water depletion differ with location and water source. In addition, most estimates of the environmental impacts of water use have focused on depletion from a single-source perspective without separating geographically different water sources. Therefore, comprehensive potential impacts from multiple water sources remain unclear. In this study, we quantified the potential impacts of the global food production on freshwater availability (water availability footprint), applying the Water Availability Factor (fwa). Each water source including rainfall, surface water, and groundwater had individual fwa, which is calculated based on the geophysical hydrological cycle, to reflect the differences among renewable freshwater resources by place and source. The fwa for each water source was estimated based on land area or time period required to obtain the reference volume of freshwater. The reference volume was regarded as 1 m3 of rainfall over an area of 1.0 m2 (1,000 mm/year), based on the global mean annual precipitation. This concept is consistent with the Ecological Footprint (EF), which measures how much biologically productive land area is required to provide the resources consumed. The EF concept is measured in global hectares, a standardized unit equal to one hectare with global average bioproductivity. We found that the current agriculture consumes freshwater resources at 1.3 times the rapid rate than sustainable water use. This rate can also indicate environmental water scarcity. Among environmentally water-scarce countries, well-financed countries tend to import cereal products as virtual water to compensate for their domestic water resources. Among water-abundant countries, well-financed countries tend to export cereal products by exploiting their freshwater availability. The fwa concept provides a non-conventional approach to compare and integrate the potential impacts of freshwater use from various sources and climatic conditions. The results should focus attention on the need to address not only physical but also social and environmental water-scarcity issues.

  9. Evidence for reduced export productivity following the Cretaceous/Paleogene mass extinction

    NASA Astrophysics Data System (ADS)

    Esmeray-Senlet, Selen; Wright, James D.; Olsson, Richard K.; Miller, Kenneth G.; Browning, James V.; Quan, Tracy M.

    2015-06-01

    The Cretaceous/Paleogene (K/Pg) mass extinction was associated with a collapse in the carbon isotopic (δ13C) gradient between planktonic and benthic foraminifera and a decrease in bulk carbonate δ13C values. These perturbations have been explained by several hypotheses: global collapse of primary productivity (Strangelove Ocean), greatly reduced export but not primary productivity (Living Ocean), little or no reduction in export productivity (Resilient Ocean), and geographic heterogeneity in the change of export productivity (Heterogeneous Ocean). We tested primary versus export productivity changes in the paleoshelf of New Jersey, where δ13C values and organic carbon accumulation rates can distinguish among different ocean responses. On the shelf, the K/Pg boundary is associated with a ~2.5‰ δ13C decrease in bulk carbonate, a ~0.8‰ δ13C decrease in organic carbon, a collapse of the surface to bottom δ13C gradient, and a drop in organic carbon accumulation rates. We interpret an early Danian ~1.0‰ planktonic foraminiferal δ13C gradient, a ~0.75‰ cross-shelf benthic foraminiferal δ13C gradient, and a drop in carbon accumulation rates to reflect the presence of active primary but limited export productivity, consistent with the Living Ocean hypothesis. We evaluated interbasinal deep-sea benthic foraminiferal δ13C gradients between the Pacific (Site 1210) and Atlantic (Site 1262) oceans as a proxy for changes in export productivity. The interbasinal δ13C gradient was reduced after the mass extinction, suggesting a reduction in global export productivity. Although our data support the Living Ocean hypothesis, evidence from paleoupwelling zones shows significant export productivity, indicating spatial heterogeneity in the wake of the K/Pg mass extinction (Heterogeneous Ocean).

  10. EFFECT OF RESIDENCE TIME ON ANNUAL EXPORT AND DENITRIFICATION OF NITROGEN IN ESTUARIES: A MODEL ANALYSIS

    EPA Science Inventory

    A simple model of annual average response of an estuary to mean nitrogen loading rate and freshwater residence time was developed and tested. It uses nitrogen inputs from land, deposition from the atmosphere, and first-order calculations of internal loss rate and export to perfor...

  11. Allelopathy in freshwater cyanobacteria.

    PubMed

    Leo, Pedro N; Vasconcelos, M Teresa S D; Vasconcelos, Vtor M

    2009-01-01

    Freshwater cyanobacteria produce several bioactive secondary metabolites with diverse chemical structure, which may achieve high concentrations in the aquatic medium when cyanobacterial blooms occur. Some of the compounds released by cyanobacteria have allelopathic properties, influencing the biological processes of other phytoplankton or aquatic plants. These kinds of interactions are more easily detectable under laboratory studies; however their ecological relevance is often debated. Recent research has discovered new allelopathic properties in some cyanobacteria species, new allelochemicals and elucidated some of the allelopathic mechanisms. Ecosystem-level approaches have shed some light on the factors that influence allelopathic interactions, as well as how cyanobacteria may be able to modulate their surrounding environment by means of allelochemical release. Nevertheless, the role of allelopathy in cyanobacteria ecology is still not well understood, and its clarification should benefit from carefully designed field studies, chemical characterization of allelochemicals and new methodological approaches at the "omics" level. PMID:19863381

  12. The Ocean-Atmosphere Hydrothermohaline Conveyor Belt

    NASA Astrophysics Data System (ADS)

    Döös, Kristofer; Kjellsson, Joakim; Zika, Jan; Laliberté, Frédéric; Brodeau, Laurent

    2015-04-01

    The ocean thermohaline circulation is linked to the hydrothermal circulation of the atmosphere. The ocean thermohaline circulation is expressed in potential temperature-salinity space and comprises a tropical upper-ocean circulation, a global conveyor belt cell and an Antarctic Bottom Water cell. The atmospheric hydrothermal circulation in a potential temperature-specific humidity space unifies the tropical Hadley and Walker cells as well as the midlatitude eddies into a single, global circulation. Superimposed, these thermohaline and hydrothermal stream functions reveal the possibility of a close connection between some parts of the water and air mass conversions. The exchange of heat and fresh water through the sea surface (precipiation-evaporation) and incoming solar radiation act to make near-surface air warm and moist while making surface water warmer and saltier as both air and water travel towards the Equator. In the tropics, air masses can undergo moist convection releasing latent heat by forming precipitation, thus acting to make warm surface water fresher. We propose that the Clausius-Clapeyron relationship for moist near-surface air acts like a lower bound for the atmospheric hydrothermal cell and an upper bound for the ocean thermohaline Conveyor-Belt cell. The analysis is made by combining and merging the overturning circulation of the ocean and atmosphere by relating the salinity of the ocean to the humidity of the atmosphere, where we set the heat and freshwater transports equal in the two stream functions By using simulations integrated with our Climate-Earth system model EC-Earth, we intend to produce the "hydrothermohaline" stream function of the coupled ocean-atmosphere overturning circulation in one single picture. We explore how the oceanic thermohaline Conveyor Belt can be linked to the global atmospheric hydrothermal circulation and if the water and air mass conversions in humidity-temperature-salinity space can be related and linked to each other along a "line" corresponding to the Clausius-Clapeyron relationship. A geographical description of how and where this occurs together with this new hydrothermohaline stream function will be searched for. The net heat and freshwater transport of the ocean and atmosphere can aslo be calculated from the thermohaline and hydrothermal stream functions. The heat transport across isohumes in the atmosphere and isohalines in the ocean as well as the freshwater transport across isotherms in both the atmosphere and ocean are computed. The maximum heat transport is about 16 PW in the atmosphere, while that of the ocean is just about 1 PW. The freshwater transport across isotherms in the atmosphere and ocean are shown to be tightly connected with a net maximum freshwater transport of 4 SV in the atmosphere and 2 Sv in the ocean.

  13. 77 FR 65667 - Freshwater Crawfish Tail Meat From the People's Republic of China: Initiation of Antidumping Duty...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-10-30

    ... the People's Republic of China, 62 FR 48218 (September 15, 1997). \\2\\ See Freshwater Crawfish Tail... separate from the country-wide rate provide evidence of de jure and de facto absence of government control... not subject to either de jure or de facto government control with respect to its export of...

  14. The puzzle of oceanic oxygen utilization

    NASA Astrophysics Data System (ADS)

    Koeve, Wolfgang; Khler, Paul

    2014-05-01

    The biological carbon pump is an important component of the oceanic carbon cycle and expected to respond to the anthropogenic perturbation of climate and ocean chemistry. Yet, large uncertainties exist in the quantification of the strength of the biological carbon pump of today's ocean. The export of organic matter from the ocean's euphotic zone is a critical benchmark number of this strength. Local measurements of the export flux are highly uncertain, due f.e. to severe methodological issues and undersampling of the ocean. Uncertainties in the contribution of dissolved organic matter to export further add when it comes to a global assessment. The vertical integral of oxygen utilization in the interior of the ocean is considered an independent and save estimate of export production, which accounts for particles as well as dissolved export pathways. For that purpose regional oxygen utilization rates (OUR) have been computed from apparent oxygen utilization (AOU) and an estimate of the time elapsed since the last contact with the atmosphere. Surprisingly the assumptions underlying this concept have not been tested rigorously. Using global ocean biogeochemical models we compare OUR computed from AOU and an ideal age tracer with an independent and perfect estimate of ocean respiration available in the model. Consistently in three different global models, we find that OUR underestimates true respiration by a factor of about three. Most of the differences between respiration and OUR are observed in the upper 1000m of the ocean. In addition to this underestimate in bulk global numbers, we find also important qualitative differences between the two independent approaches. For example, the contribution of dissolved organic matter driving oxygen utilization is largely underestimated when based on bulk tracer concentrations (AOU, DOC), which is the usual approach applied to observations. Also, diagnosing the global importance of denitrification relative to oxic metabolism is found to be uncertain by a factor of three when based on analysis of bulk tracers.

  15. Role of the ocean in controlling atmospheric CO2 concentration in the course of global glaciations

    NASA Astrophysics Data System (ADS)

    Oka, Akira; Tajika, Eiichi; Abe-Ouchi, Ayako; Kubota, Keiko

    2011-11-01

    Responses of ocean circulation and ocean carbon cycle in the course of a global glaciation from the present Earth conditions are investigated by using a coupled climate-biogeochemical model. We investigate steady states of the climate system under colder conditions induced by a reduction of solar constant from the present condition. A globally ice-covered solution is obtained under the solar constant of 92.2% of the present value. We found that because almost all of sea water reaches the frozen point, the ocean stratification is maintained not by temperature but by salinity just before the global glaciation (at the solar constant of 92.3%). It is demonstrated that the ocean circulation is driven not by the surface cooling but by the surface freshwater forcing associated with formation and melting of sea ice. As a result, the deep ocean is ventilated exclusively by deep water formation in southern high latitudes where sea ice production takes place much more massively than northern high latitudes. We also found that atmospheric CO2 concentration decreases through the ocean carbon cycle. This reduction is explained primarily by an increase of solubility of CO2 due to a decrease of sea surface temperature, whereas the export production weakens by 30% just before the global glaciation. In order to investigate the conditions for the atmospheric CO2 reduction to cause global glaciations, we also conduct a series of simulations in which the total amount of carbon in the atmosphere-ocean system is reduced from the present condition. Under the present solar constant, the results show that the global glaciation takes place when the total carbon decreases to be 70% of the present-day value. Just before the glaciation, weathering rate becomes very small (almost 10% of the present value) and the organic carbon burial declines due to weakened biological productivity. Therefore, outgoing carbon flux from the atmosphere-ocean system significantly decreases. This suggests the atmosphere-ocean system has strong negative feedback loops against decline of the total carbon content. The results obtained here imply that some processes outside the atmosphere-ocean feedback loops may be required to cause global glaciations.

  16. The Southern Ocean silica cycle

    NASA Astrophysics Data System (ADS)

    Trguer, Paul J.

    2014-11-01

    The Southern Ocean is a major opal sink and plays a key role in the silica cycle of the world ocean. So far however, a complete cycle of silicon in the Southern Ocean has not been published. On one hand, Southern Ocean surface waters receive considerable amounts of silicic acid (dissolved silica, DSi) from the rest of the world ocean through the upwelling of the Circumpolar Deep Water, fed by contributions of deep waters of the Atlantic, Indian, and Pacific Oceans. On the other hand, the Southern Ocean exports a considerable flux of the silicic acid that is not used by diatoms in surface waters through the northward pathways of the Sub-Antarctic Mode Water, of the Antarctic Intermediate Water, and of the Antarctic Bottom Water. Thus the Southern Ocean is a source of DSi for the rest of the world ocean. Here we show that the Southern Ocean is a net importer of DSi: because there is no significant external input of DSi, the flux of DSi imported through the Circumpolar Deep Water pathway compensates the sink flux of biogenic silica in sediments.

  17. Carbon export algorithm advancements in models

    NASA Astrophysics Data System (ADS)

    Çağlar Yumruktepe, Veli; Salihoğlu, Barış

    2015-04-01

    The rate at which anthropogenic CO2 is absorbed by the oceans remains a critical question under investigation by climate researchers. Construction of a complete carbon budget, requires better understanding of air-sea exchanges and the processes controlling the vertical and horizontal transport of carbon in the ocean, particularly the biological carbon pump. Improved parameterization of carbon sequestration within ecosystem models is vital to better understand and predict changes in the global carbon cycle. Due to the complexity of processes controlling particle aggregation, sinking and decomposition, existing ecosystem models necessarily parameterize carbon sequestration using simple algorithms. Development of improved algorithms describing carbon export and sequestration, suitable for inclusion in numerical models is an ongoing work. Existing unique algorithms used in the state-of-the art ecosystem models and new experimental results obtained from mesocosm experiments and open ocean observations have been inserted into a common 1D pelagic ecosystem model for testing purposes. The model was implemented to the timeseries stations in the North Atlantic (BATS, PAP and ESTOC) and were evaluated with datasets of carbon export. Targetted topics of algorithms were PFT functional types, grazing and vertical movement of zooplankton, and remineralization, aggregation and ballasting dynamics of organic matter. Ultimately it is intended to feed improved algorithms to the 3D modelling community, for inclusion in coupled numerical models.

  18. Interdecadal variability of Northeast Pacific coastal freshwater and its implications on biological productivity

    NASA Astrophysics Data System (ADS)

    Royer, Thomas C.; Grosch, Chester E.; Mysak, Lawrence A.

    The coastal freshwater discharge along the northern Gulf of Alaska has been determined using a simple hydrology model for 1931-1999, and through the use of autocorrelative and spectral techniques oscillations were discovered with significant periods of 0.5, 1, 1.2 and 16-20 years. Changes in the freshwater discharge are well correlated with hydrographic properties, namely temperature and salinity, at a coastal site near Seward, Alaska. Changes in the salinity should change the vertical stability, which will affect the mixed layer depth and primary production. Changes in the mixed layer depth concurrent with changes in phytoplankton production may provide a link between zooplankton and freshwater discharge. This is supported by periodicities of 0.5, 1 and 1.2 years that have been found in the zooplankton at Ocean Station P. A positive atmosphere-ocean feedback loop is proposed that could maintain accelerated coastal freshwater discharge at periods similar to those seen in the Pacific Decadal Oscillation (PDO). This could provide a mechanism that links the PDO with coastal freshwater discharge and consequently relates coastal freshwater discharge to salmon production in Alaska, since the latter depends on zooplankton abundance.

  19. Contribution of glacier runoff to freshwater discharge into the Gulf of Alaska

    USGS Publications Warehouse

    Neal, E.G.; Hood, E.; Smikrud, K.

    2010-01-01

    Watersheds along the Gulf of Alaska (GOA) are undergoing climate warming, glacier volume loss, and shifts in the timing and volume of freshwater delivered to the eastern North Pacific Ocean. We estimate recent mean annual freshwater discharge to the GOA at 870 km3 yr-1. Small distributed coastal drainages contribute 78% of the freshwater discharge with the remainder delivered by larger rivers penetrating coastal ranges. Discharge from glaciers and icefields accounts for 47% of total freshwater discharge, with 10% coming from glacier volume loss associated with rapid thinning and retreat of glaciers along the GOA. Our results indicate the region of the GOA from Prince William Sound to the east, where glacier runoff contributes 371 km3 yr -1, is vulnerable to future changes in freshwater discharge as a result of glacier thinning and recession. Changes in timing and magnitude of freshwater delivery to the GOA could impact coastal circulation as well as biogeochemical fluxes to near-shore marine ecosystems and the eastern North Pacific Ocean. Copyright ?? 2010 by the American Geophysical Union.

  20. Contrasting size evolution in marine and freshwater diatoms.

    PubMed

    Litchman, E; Klausmeier, C A; Yoshiyama, K

    2009-02-24

    Diatoms are key players in the global carbon cycle and most aquatic ecosystems. Their cell sizes impact carbon sequestration and energy transfer to higher trophic levels. We report fundamental differences in size distributions of marine and freshwater diatoms, with marine diatoms significantly larger than freshwater species. An evolutionary game theoretical model with empirical allometries of growth and nutrient uptake shows that these differences can be explained by nitrogen versus phosphorus limitation, nutrient fluctuations and mixed layer depth differences. Constant and pulsed phosphorus supply select for small sizes, as does constant nitrogen supply. In contrast, intermediate frequency nitrogen pulses common in the ocean select for large sizes or the evolutionarily stable coexistence of large and small sizes. Size-dependent sinking interacts with mixed layer depth (MLD) to further modulate optimal sizes, with smaller sizes selected for by strong sinking and shallow MLD. In freshwaters, widespread phosphorus limitation, together with strong sinking and shallow MLD produce size distributions with smaller range, means and upper values, compared with the ocean. Shifting patterns of nutrient limitation and mixing may alter diatom size distributions, affecting global carbon cycle and the structure and functioning of aquatic ecosystems. PMID:19202058

  1. Contrasting size evolution in marine and freshwater diatoms

    PubMed Central

    Litchman, E.; Klausmeier, C. A.; Yoshiyama, K.

    2009-01-01

    Diatoms are key players in the global carbon cycle and most aquatic ecosystems. Their cell sizes impact carbon sequestration and energy transfer to higher trophic levels. We report fundamental differences in size distributions of marine and freshwater diatoms, with marine diatoms significantly larger than freshwater species. An evolutionary game theoretical model with empirical allometries of growth and nutrient uptake shows that these differences can be explained by nitrogen versus phosphorus limitation, nutrient fluctuations and mixed layer depth differences. Constant and pulsed phosphorus supply select for small sizes, as does constant nitrogen supply. In contrast, intermediate frequency nitrogen pulses common in the ocean select for large sizes or the evolutionarily stable coexistence of large and small sizes. Size-dependent sinking interacts with mixed layer depth (MLD) to further modulate optimal sizes, with smaller sizes selected for by strong sinking and shallow MLD. In freshwaters, widespread phosphorus limitation, together with strong sinking and shallow MLD produce size distributions with smaller range, means and upper values, compared with the ocean. Shifting patterns of nutrient limitation and mixing may alter diatom size distributions, affecting global carbon cycle and the structure and functioning of aquatic ecosystems. PMID:19202058

  2. Arctic Ocean circulation during the anoxic Eocene Azolla event

    NASA Astrophysics Data System (ADS)

    Speelman, Eveline; Sinninghe Damst, Jaap; Mrz, Christian; Brumsack, Hans; Reichart, Gert-Jan

    2010-05-01

    The Azolla interval, as encountered in Eocene sediments from the Arctic Ocean, is characterized by organic rich sediments ( 4wt% Corg). In general, high levels of organic matter may be caused by increased productivity, i.e. extensive growth of Azolla, and/or enhanced preservation of organic matter, or a combination of both. Anoxic (bottom) water conditions, expanded oxygen minimum zones, or increased sedimentation rates all potentially increase organic matter preservation. According to plate tectonic, bathymetric, and paleogeographic reconstructions, the Arctic Ocean was a virtually isolated shallow basin, with one possible deeper connection to the Nordic Seas represented by a still shallow Fram Strait (Jakobsson et al., 2007), hampering ventilation of the Arctic Basin. During the Azolla interval surface waters freshened, while at the same time bottom waters appear to have remained saline, indicating that the Arctic was highly stratified. The restricted ventilation and stratification in concert with ongoing export of organic matter most likely resulted in the development of anoxic conditions in the lower part of the water column. Whereas the excess precipitation over evaporation maintained the freshwater lid, sustained input of Nordic Sea water is needed to keep the deeper waters saline. To which degree the Arctic Ocean exchanged with the Nordic Seas is, however, still largely unknown. Here we present a high-resolution trace metal record (ICP-MS and ICP-OES) for the expanded Early/Middle Eocene section capturing the Azolla interval from Integrated Ocean Drilling Program (IODP) Expedition 302 (ACEX) drilled on the Lomonosov Ridge, central Arctic Ocean. Euxinic conditions throughout the interval resulted in the efficient removal of redox sensitive trace metals from the water column. Using the sedimentary trace metal record we also constrained circulation in the Arctic Ocean by assessing the relative importance of trace metal input sources (i.e. fluvial, eolian, and through seawater inflow). Excess vanadium accumulation during the Azolla event (80 ppm), basin volume and surface area, average vanadium sea (1.8 ppb) and river water (1.0 ppb) concentrations, together indicate that an inflow of Nordic Sea water of 0.2 Sv is needed to sustain vanadium levels. The same calculation using molybdenum gives an inflow of only 0.02 Sv. These low inflow rates imply Arctic Ocean (deep) water residence times of 2000 - 20000 years, respectively. Based on climate modeling we calculated a summed net amount of precipitation for the Eocene Arctic Basin (Precipitation - Evaporation + Runoff) of 0.46 Sv. Together these notions indicate that a compensating inflow of saline North Atlantic water occurred, accompanied by an outflow of more fresh waters, resulting in a bi-directional, two-layer flow through the (proto-) Fram Strait. Consequently, the limited exchange of water through the Fram Strait implies that a relatively low export productivity would have been sufficient to render Arctic bottom waters anoxic. Jakobsson, M., Backman, J., Rudels, B., Nycander, J., Frank, M., Mayer, L., Jokat, W., Sangiorgi, F., O'Regan, M., Brinkhuis, H., King, J., Moran, K. (2007). The early Miocene onset of a ventilated circulation regimen in the Arctic Ocean. Nature 447, 986-990.

  3. Forests fuel fish growth in freshwater deltas

    PubMed Central

    Tanentzap, Andrew J.; Szkokan-Emilson, Erik J.; Kielstra, Brian W.; Arts, Michael T.; Yan, Norman D.; Gunn, John M.

    2014-01-01

    Aquatic ecosystems are fuelled by biogeochemical inputs from surrounding lands and within-lake primary production. Disturbances that change these inputs may affect how aquatic ecosystems function and deliver services vital to humans. Here we test, using a forest cover gradient across eight separate catchments, whether disturbances that remove terrestrial biomass lower organic matter inputs into freshwater lakes, thereby reducing food web productivity. We focus on deltas formed at the stream-lake interface where terrestrial-derived particulate material is deposited. We find that organic matter export increases from more forested catchments, enhancing bacterial biomass. This transfers energy upwards through communities of heavier zooplankton, leading to a fourfold increase in weights of planktivorous young-of-the-year fish. At least 34% of fish biomass is supported by terrestrial primary production, increasing to 66% with greater forest cover. Habitat tracers confirm fish were closely associated with individual catchments, demonstrating that watershed protection and restoration increase biomass in critical life-stages of fish. PMID:24915965

  4. Methane cycling in a tidal freshwater swamp

    SciTech Connect

    Megonigal, J.P.; Schlesinger, W.H. )

    1993-06-01

    Previous studies of methanogenesis in a tidal freshwater swamp on the North Carolina coast have found that potential rates of methane production overestimate observed rates of methane flux, especially during summer months. This research investigates three possibilities for the unexplained losses: methane oxidation, lateral export of dissolved methane to the adjacent river, and ebullition. It is possible that each of these sinks increase during the summer. The potential for methane oxidation was demonstrated in intact soil cores incubated for 21 hours under a 0.5% CH[sub 3]F atmosphere. Methane flux increased from 10+/-27 (mean+/-sd) to 60+/-3 mg m[sup [minus]2] d[sup [minus]1] in treated cores; control core fluxes were 15+/-3 and 19+/-3 mg m[sup [minus]2] d[sup [minus]1] over the same periods. Incubations of slightly unsaturated soils with [sup 14]CH[sub 4] confirmed rapid potential rates of methane oxidation.

  5. Freshwater Variability between Ellesmere Island and the North Pole

    NASA Astrophysics Data System (ADS)

    Smethie, W. M.; Schlosser, P.; Newton, R.; Friedrich, R.; Steele, M.

    2013-12-01

    The Switchyard Project has established a time series of CTD and chemical measurements between Ellesmere Island and the North Pole and annual observations have been taken since 2005 to the present. The total freshwater inventory and inventories of the freshwater components (meteoric water [MEW], sea-ice melt water [SIMW] and inflow from the Pacific Ocean [PFW]) are determined from measurements of temperature, salinity, delta O-18, nitrate and phosphate, each year. The total inventory has varied by about 5 m between 2005 and 2013, which is about 50% of the lowest inventory. The total inventory was fairly stable between 2003 - 2007, then increased dramatically between 2007 and 2008 and again between 2008 and 2009. It then decreased between 2009 and 2011 and increased from 2011 to 2013. The increase between 2007 and 2008 resulted primarily from an increase in MEW tempered by decreases in SIMW and PFW. Back tracks of ice flow suggested that these waters came from the Russian continental shelves via the Transpolar Drift along the Lomonosov Ridge. The continued freshening in 2009 corresponded with a change is the large scale circulation of the Canada Basin with a weakening of the Beaufort Gyre and expulsion of freshwater, which included water from the large sea ice melting event of 2007. SIMW accounted for about two-thirds of the freshening. Ice back tracks suggest that water flowed out of the Beaufort Sea in an anticylonic pattern and crossed the Canada Basin along the Mendelev Ridge to reach the Lincoln Sea with a transport time of 2-3 years. The freshwater decrease between 2010 and 2011 was the result of a 70% decrease in SIMW and 30% decrease in MEW and the ice track flow pattern had shifted back to the pattern prior to 2009. The source of freshwater for the increase in freshwater inventory between 2011 and 2013 was MEW. PFW retreated to the continental shelf of Ellesmere Island, decreasing by about 30% and SIMW decreased to more negative values indicating water flowing into the region had been subjected to substantial sea ice formation, removing freshwater. There was a major decrease in sea ice in the summer of 2012, reaching values lower than the 2007 event. A pulse of freshwater from sea ice melt was observed two years later as discussed above. It will be interesting see if a pulse is observed in 2014, but the flow pathways may be different now than during the 2009-2010 period when sea ice and presumably surface water were exiting the Beaufort Gyre in an anticyclonic flow.

  6. Measuring Ocean Literacy: What teens understand about the ocean using the Survey of Ocean Literacy and Engagement (SOLE)

    NASA Astrophysics Data System (ADS)

    Greely, T. M.; Lodge, A.

    2009-12-01

    Ocean issues with conceptual ties to science and global society have captured the attention, imagination, and concern of an international audience. Climate change, over fishing, marine pollution, freshwater shortages and alternative energy sources are a few ocean issues highlighted in our media and casual conversations. The ocean plays a role in our life in some way everyday, however, disconnect exists between what scientists know and the public understands about the ocean as revealed by numerous ocean and coastal literacy surveys. While the public exhibits emotive responses through care, concern and connection with the ocean, there remains a critical need for a baseline of ocean knowledge. However, knowledge about the ocean must be balanced with understanding about how to apply ocean information to daily decisions and actions. The present study analyzed underlying factors and patterns contributing to ocean literacy and reasoning within the context of an ocean education program, the Oceanography Camp for Girls. The OCG is designed to advance ocean conceptual understanding and decision making by engagement in a series of experiential learning and stewardship activities from authentic research settings in the field and lab. The present study measured a) what understanding teens currently hold about the ocean (content), b) how teens feel toward the ocean environment (environmental attitudes and morality), and c) how understanding and feelings are organized when reasoning about ocean socioscientific issues (e.g. climate change, over fishing, energy). The Survey of Ocean Literacy and Engagement (SOLE), was used to measure teens understanding about the ocean. SOLE is a 57-item survey instrument aligned with the Essential Principles and Fundamental Concepts of Ocean Literacy (NGS, 2007). Rasch analysis was used to refine and validate SOLE as a reasonable measure of ocean content knowledge (reliability, 0.91). Results revealed that content knowledge and environmental attitudes significantly contributed to ocean literacy. Teens demonstrated a 2-32% increase in content knowledge following the OCG learning experience. The most significant content gains correlated with ocean literacy Essential Principles 1, 2 and 5. Analysis of environmental reasoning patterns revealed that biocentric reasoning (71%) was most important to teens in solving ocean dilemmas. Further, teens reasoning about challenging ocean dilemmas were capable of supporting a position, counter-argument, rebuttal, and accurately use scientific information. Findings provide empirical evidence that connects field studies with ocean literacy. Current guidelines for ocean literacy address cognitive understanding but lack multimodality. The need for ocean literacy that goes beyond content to include reasoning and actions is relevant towards preparing students, teachers and citizens to regularly contribute to decisions about ocean issues and undertake actions as consumer, citizen or steward. This research supports the use of socioscientific issues and stewardship to advance ‘functional’ ocean literacy.

  7. Representing Greenland ice sheet freshwater fluxes in climate models

    NASA Astrophysics Data System (ADS)

    Lenaerts, Jan T. M.; Le Bars, Dewi; Kampenhout, Leo; Vizcaino, Miren; Enderlin, Ellyn M.; Broeke, Michiel R.

    2015-08-01

    Here we present a long-term (1850-2200) best estimate of Greenland ice sheet (GrIS) freshwater runoff that improves spatial detail of runoff locations and temporal resolution. Ice discharge is taken from observations since 2000 and assumed constant in time. Surface meltwater runoff is retrieved from regional climate model output for the recent past and parameterized for the future based on significant correlations between runoff and midtropospheric (500 hPa) summer temperature changes over the GrIS. The simplicity of this approach enables assimilation of meltwater runoff into coupled climate models, which is demonstrated here in a case study with the medium-resolution (1°) Community Earth System Model. The model results suggest that the decrease in Atlantic Meridional Overturning Circulation (AMOC) is dominated by warming of the surface ocean and enhanced GrIS freshwater forcing leads to a slightly enhanced (-1.2 sverdrup in the 21st century) weakening of the AMOC.

  8. Accelerated drawdown of meridional overturning in the late-glacial Atlantic triggered by transient pre-H event freshwater perturbation

    NASA Astrophysics Data System (ADS)

    Hall, I. R.; Moran, S. B.; Zahn, R.; Knutz, P. C.; Shen, C.-C.; Edwards, R. L.

    2006-08-01

    Abrupt decreases of the Atlantic meridional overturning circulation (MOC) during the Late Pleistocene have been directly linked to catastrophic discharges of glacimarine freshwater, triggering disruption of northward marine heat transport and causing global climate changes. Here we provide measurements of excess sedimentary 231Pa/230Th from a high-accumulation sediment drift deposit in the NE Atlantic that record a sequence of sudden variations in the rate of MOC, associated deep ocean ventilation and surface-ocean climatology. The data series reveal a sequential decrease in the MOC rate at ~18.0 ka BP ago that coincides with only transient and localized freshwater inputs. This change represents a substantial, though not total, cessation in MOC that predates the major Heinrich (H1) meltwater event by at least 1,200 years. These results highlight the potential of targeted freshwater perturbations in promoting substantial MOC changes without a direct linking with catastrophic freshwater surges.

  9. A twentieth-century reanalysis forced ocean model to reconstruct the North Atlantic climate variation during the 1920s

    NASA Astrophysics Data System (ADS)

    Mller, W. A.; Matei, D.; Bersch, M.; Jungclaus, J. H.; Haak, H.; Lohmann, K.; Compo, G. P.; Sardeshmukh, P. D.; Marotzke, J.

    2015-04-01

    The observed North Atlantic multi-decadal variability for the period 1872-2009 is reconstructed with the Max Planck Institute ocean model, which is forced with an ensemble of the atmospheric twentieth century reanalysis. Special emphasis is put on the early part of the experiments, which includes a prominent climate variation during the 1920s. The experiments are in agreement with selected hydrographic records, indicating a transition from cold and fresh North Atlantic water properties, prior to the 1920 climate variation, towards warm and saline waters afterwards. Examining the variation reveals that sea level pressure (SLP) anomalies prior to the 1900s resemble a negative phase of North Atlantic Oscillation and associated weak winds result in a weak North Atlantic Current (NAC) and sub-polar gyre (SPG). This leads to a reduced transport of warm and saline waters into the higher latitudes. Simultaneously, Arctic freshwater release results in the accumulation of cold and fresh water properties, which cover the upper layers in the Labrador Sea and subsequently suppress convection. From the 1910s, the Arctic freshwater export is reduced, and, NAC and SPG are strengthened as a result of an increased SLP gradient over the North Atlantic. Concurrently, Labrador Sea convection and Atlantic meridional overturning circulation (AMOC) increase. The intensified NAC, SPG, and AMOC redistribute sub-tropical water into the North Atlantic and Nordic Seas, thereby increasing observed and modelled temperature and salinity during the 1920s.

  10. High-resolution modelling of the shelf and open ocean adjacent to South Georgia, Southern Ocean

    NASA Astrophysics Data System (ADS)

    Young, Emma F.; Meredith, Michael P.; Murphy, Eugene J.; Carvalho, Gary R.

    2011-07-01

    The marine ecosystem on the shelf and open ocean adjacent to South Georgia is extraordinarily rich, with a history of commercial exploitation. Although much progress has been made, attempts at modelling (and hence better understanding) this system have consistently been hampered by the poor representation of key physical processes in global or regional ocean general circulation models. Here we present the development of a high-resolution 3D hydrodynamic model of the South Georgia shelf and the adjacent open ocean, including a novel method for prescribing freshwater fluxes. The ability of the model to reproduce the observed oceanography of the region is quantified by comparisons with data from tide gauges at South Georgia, with satellite-derived sea surface temperatures, and with an extensive CTD dataset collected during January-April 1995. Predicted cotidal charts for the diurnal tides O 1 and K 1 show a periodic amplification in both the current and elevation fields at the shelf edge, suggesting the presence of a diurnally forced continental shelf wave. This could have important implications for processes such as larval transport and retention. The comparison with CTD data reveals mean and root mean square errors in temperature (salinity) of -0.27 °C (-0.07) and 0.64 °C (0.23), respectively. Vertical profiles of potential temperature and salinity on the shelf agree acceptably well with observations, but there is a tendency for the model to under-predict the density contrast between surface and bottom waters. The main limitation on model accuracy is found to be the large-scale forcing. Releasing a passive tracer into the model, transport and retention pathways are identified, including a prevalence for tracer export from the shelf to the west of South Georgia, and a transport pathway linking South Georgia and Shag Rocks. Significantly, the model suggests this to be a unidirectional link, from South Georgia to Shag Rocks, with possible significance for fisheries management. The implications of these results in the context of the South Georgia ecosystem are discussed briefly, demonstrating the usefulness of this new tool for interdisciplinary studies of the region.

  11. Response of Thermohaline Circulation to Freshwater Forcing under Present Day and LGM Conditions

    NASA Astrophysics Data System (ADS)

    Hu, A.; Otto-Bliesner, B. L.; Meehl, G. A.; Han, W.; Morrill, C.; Brady, E. C.; Briegleb, B.

    2007-12-01

    Responses of the thermohaline circulation (THC) to freshwater forcing (hosing) in the subpolar North Atlantic Ocean under present day and the last glacial maximum (LGM) conditions are investigated using the National Center for Atmospheric Research Community Climate System Model versions 2 and 3. Three sets of simulations are analyzed, with each set including a control run and a freshwater hosing run. The first two sets are under present day conditions with an open and closed Bering Strait. The third one is under LGM conditions, which has a closed Bering Strait. Results show that the THC nearly collapses in all three hosing runs when the freshwater forcing is turned on. The full recovery of the THC, however, is at least a century earlier in the open Bering Strait run than the closed Bering Strait and LGM runs. This is because the excessive freshwater is diverged almost equally towards north and south from the subpolar North Atlantic when the Bering Strait is open. A significant portion of the freshwater flowing northward into the Arctic exits into the North Pacific via a reversed Bering Strait throughflow, which accelerates the THC recovery. When the Bering Strait is closed, this Arctic to Pacific transport is absent and freshwater can only be removed through the southern end of the North Atlantic. Together with the surface freshwater excess due to precipitation, evaporation, river runoff, and melting ice in the closed Bering Strait experiments after the hosing, the removal of the excessive freshwater takes longer, and this slows the recovery of the THC. Although the background conditions are quite different between the present day closed Bering Strait run and the LGM run, the THC responds to the freshwater forcing added in the North Atlantic in a very similar manner.

  12. Removing the North Pacific halocline: Effects on global climate, ocean circulation and the carbon cycle

    NASA Astrophysics Data System (ADS)

    Menviel, L.; Timmermann, A.; Elison Timm, O.; Mouchet, A.; Abe-Ouchi, A.; Chikamoto, M. O.; Harada, N.; Ohgaito, R.; Okazaki, Y.

    2012-02-01

    A well-pronounced halocline is a key feature of today's subarctic North Pacific. There is indirect paleo-evidences from the last glacial termination as well as from the early and middle Pliocene that this halocline has not always been there. To study the effects of North Pacific salinity on global climate, ocean circulation and the marine carbon cycle, we perform idealized experiments using an Earth system model of intermediate complexity (LOVECLIM). Imposing a negative freshwater flux in the northern North Pacific, the halocline vanishes and a deep Pacific meridional overturning circulation (PMOC) establishes. The associated increase of meridional heat transport in the Pacific leads to a bipolar seesaw response in temperature, with warming in the North Pacific and over North America and cooling in the Southern Ocean. As a result of the formation of North Pacific deep water (NPDW), the surface branch of the global conveyor belt circulation weakens. Transport through the Indonesian Seas decreases by 50% as the warm and saline waters of the equatorial Pacific are diverted into the North Pacific. In our idealized experiments, the enhanced global deep water formation is balanced by an increase in diapycnal mixing. As a result nutrient concentrations in the euphotic zone increase by about 25% globally, leading to a 20% increase in global export production. The effect of greater export production on atmospheric pCO2 is, however, compensated by the enhanced transport of dissolved inorganic carbon (DIC) to the surface. As a result, the atmospheric CO2 concentration increases by only 5 ppmv. Our results further suggest that the absence of the subarctic halocline for instance during Heinrich event 1 and the Pliocene may have exerted a strong influence on global climate and the carbon cycle.

  13. Inhabitants of the Fresh-Water Community.

    ERIC Educational Resources Information Center

    Jorgensen, Joseph; Schroeder, Marlene

    This learner's guide is designed to assist middle school students in studying freshwater organisms. Following a brief introduction to freshwater ecology, simple line drawings facilitate the identification of plants and animals common to Florida's freshwater ecosystems. Emphasis of the short text which accompanies each illustration is upon the…

  14. Inhabitants of the Fresh-Water Community.

    ERIC Educational Resources Information Center

    Jorgensen, Joseph; Schroeder, Marlene

    This learner's guide is designed to assist middle school students in studying freshwater organisms. Following a brief introduction to freshwater ecology, simple line drawings facilitate the identification of plants and animals common to Florida's freshwater ecosystems. Emphasis of the short text which accompanies each illustration is upon the

  15. The sensitivity of the climate response to the magnitude and location of freshwater forcing: last glacial maximum experiments

    NASA Astrophysics Data System (ADS)

    Otto-Bliesner, Bette L.; Brady, Esther C.

    2010-01-01

    Proxy records indicate that the locations and magnitudes of freshwater forcing to the Atlantic Ocean basin as iceberg discharges into the high-latitude North Atlantic, Laurentide meltwater input to the Gulf of Mexico, or meltwater diversion to the North Atlantic via the St. Lawrence River and other eastern outlets may have influenced the North Atlantic thermohaline circulation and global climate. We have performed Last Glacial Maximum (LGM) simulations with the NCAR Community Climate System Model (CCSM3) in which the magnitude of the freshwater forcing has been varied from 0.1 to 1 Sv and inserted either into the subpolar North Atlantic Ocean or the Gulf of Mexico. In these glacial freshening experiments, the less dense freshwater provides a lid on the ocean water below, suppressing ocean convection and interaction with the atmosphere above and reducing the Atlantic Meridional Overturning Circulation (AMOC). This is the case whether the freshwater is added directly to the area of convection south of Greenland or transported there by the subtropical and subpolar gyres when added to the Gulf of Mexico. The AMOC reduction is less for the smaller freshwater forcings, but is not linear with the size of the freshwater perturbation. The recovery of the AMOC from a "slow" state is ˜200 years for the 0.1 Sv experiment and ˜500 years for the 1 Sv experiment. For glacial climates, with large Northern Hemisphere ice sheets and reduced greenhouse gases, the cold subpolar North Atlantic is primed to respond rapidly and dramatically to freshwater that is either directly dumped into this region or after being advected from the Gulf of Mexico. Greenland temperatures cool by 6-8 °C in all the experiments, with little sensitivity to the magnitude, location or duration of the freshwater forcing, but exhibiting large seasonality. Sea ice is important for explaining the responses. The Northern Hemisphere high latitudes are slow to recover. Antarctica and the Southern Ocean show a bipolar response, with warming and reduced sea ice. This warming continues after the cessation of the freshwater forcing and shows a dependence on the duration of the freshwater forcing. Equatorward of the expanded sea ice, the simulated temperature and salinity anomalies are sensitive to the amount of colder and fresher waters that are advected out of the subpolar North Atlantic. In the tropical Atlantic, the recovery of the Intertropical Convergence Zone (ITCZ) from its more southerly position during the freshwater forcing is much more rapid than the recovery of the AMOC, and is more related to the recovery of low-latitude surface temperatures than Greenland temperature or sea ice. These results have implications for using proxy records as indirect measures of the AMOC.

  16. Improving estuarine net flux estimates for dissolved cadmium export at the annual timescale: Application to the Gironde Estuary

    NASA Astrophysics Data System (ADS)

    Dabrin, Aymeric; Schfer, Jrg; Blanc, Grard; Strady, Emilie; Masson, Matthieu; Bossy, Ccile; Castelle, Sabine; Girardot, Nag; Coynel, Alexandra

    2009-10-01

    Dissolved Cd (Cd D) concentrations along the salinity gradient were measured in surface water of the Gironde Estuary during 15 cruises (2001-2007), covering a wide range of contrasting situations in terms of hydrology, turbidity and season. During all situations dissolved Cd concentrations displayed maximum values in the mid-salinity range, reflecting Cd addition by chloride-induced desorption and complexation. The daily net Cd D fluxes from the Gironde Estuary to the coastal ocean were estimated using Boyle's method. Extrapolating Cd D concentrations in the high salinity range to the freshwater end member using a theoretical dilution line produced 15 theoretical Cd concentrations (Cd D0), each representative of one distinct situation. The obtained Cd D0 concentrations were relatively similar (201 28 ng L -1) when freshwater discharge Q was >500 m 3 s -1 (508 ? Q ? 2600 m 3 s -1), but were highly variable (340 80 ng L -1; 247-490 ng L -1) for low discharge situations (169 ? Q ? 368 m 3 s -1). The respective daily Cd D net fluxes were 5-39 kg day -1, mainly depending on freshwater discharge. As this observation invalidates the existing method of estimating annual Cd D net fluxes, we proposed an empirical model, using representative Cd D0 values and daily freshwater discharges for the 2001-2007 period. Subsequent integration produced reliable Cd D net flux estimates for the Gironde Estuary at the annual timescale that ranged between 3.8-5.0 t a -1 in 2005 and 6.0-7.2 t a -1 in 2004, depending on freshwater discharge. Comparing Cd D net fluxes with the incoming Cd D fluxes suggested that the annual net Cd D addition in the Gironde Estuary ranged from 3.5 to 6.7 t a -1, without any clear temporal trend during the past seven years. The annual Cd D net fluxes did not show a clearly decreasing trend in spite of an overall decrease by a factor 6 in Cd gross fluxes during the past decade. Furthermore, in six years out of seven (except 2003), the annual Cd D net fluxes even exceeded river borne total (dissolved + particulate) gross Cd fluxes into the estuary. These observations were attributed to progressive Cd desorption from both suspended particles and bottom sediment during various sedimentation-resuspension cycles induced by tidal currents and/or continuous dredging (navigation channel) and diverse intra-estuarine sources (wet deposition, urban sources, and agriculture). Provided that gross fluxes remain stable over time, dissolved Cd exportation from the Gironde Estuary to the coastal ocean may remain at the present level for the coming decade and the estuarine sedimentary Cd stock is forecast to decrease slowly.

  17. Diverse migration strategy between freshwater and seawater habitats in the freshwater eel genus Anguilla.

    PubMed

    Arai, T; Chino, N

    2012-07-01

    The freshwater eels of the genus Anguilla, which are catadromous, migrate between freshwater growth habitats and offshore spawning areas. A number of recent studies, however, found examples of the temperate species Anguilla anguilla, Anguilla rostrata, Anguilla japonica, Anguilla australis and Anguilla dieffenbachii that have never migrated into fresh water, spending their entire life history in the ocean. Furthermore, those studies found an intermediate type between marine and freshwater residents, which appear to frequently move between different environments during their growth phase. The discovery of marine and brackish-water residents Anguilla spp. suggests that they do not all have to be catadromous, and it calls into question the generalized classification of diadromous fishes. There has been little available information, however, concerning migration in tropical Anguilla spp. Anguilla marmorata, shows three fluctuation patterns: (1) continuous residence in fresh water, (2) continuous residence in brackish water and (3) residence in fresh water after recruitment, while returning to brackish water. Such migratory patterns were found in other tropical species, Anguilla bicolor bicolor and Anguilla bicolor pacifica. In A. b. bicolor collected in a coastal lagoon of Indonesia, two further patterns of habitat use were found: (1) constantly living in either brackish water or sea water with no freshwater life and (2) habitat shift from fresh water to brackish water or sea water. The wide range of environmental habitat use indicates that migratory behaviour of tropical Anguilla spp. is facultative among fresh, brackish and marine waters during their growth phases after recruitment to the coastal areas. Further, the migratory behaviours of tropical Anguilla spp. appear to differ in each habitat in response to inter and intra-specific competition. The results suggest that tropical Anguilla spp. have a flexible pattern of migration, with an ability to adapt to various habitats and salinities. The ability of anguillids to reside in environments of various salinities would be a common feature between tropical and temperate species without a latitudinal cline. Thus, the migration of Anguilla spp. into fresh water is clearly not an obligatory behaviour. This evidence of geographical variability among Anguilla spp. suggests that habitat use is determined by environmental conditions in each site. PMID:22803719

  18. Cable Bacteria in Freshwater Sediments.

    PubMed

    Risgaard-Petersen, Nils; Kristiansen, Michael; Frederiksen, Rasmus B; Dittmer, Anders Lindequist; Bjerg, Jesper Tataru; Trojan, Daniela; Schreiber, Lars; Damgaard, Lars Riis; Schramm, Andreas; Nielsen, Lars Peter

    2015-09-01

    In marine sediments cathodic oxygen reduction at the sediment surface can be coupled to anodic sulfide oxidation in deeper anoxic layers through electrical currents mediated by filamentous, multicellular bacteria of the Desulfobulbaceae family, the so-called cable bacteria. Until now, cable bacteria have only been reported from marine environments. In this study, we demonstrate that cable bacteria also occur in freshwater sediments. In a first step, homogenized sediment collected from the freshwater stream Giber Å, Denmark, was incubated in the laboratory. After 2 weeks, pH signatures and electric fields indicated electron transfer between vertically separated anodic and cathodic half-reactions. Fluorescence in situ hybridization revealed the presence of Desulfobulbaceae filaments. In addition, in situ measurements of oxygen, pH, and electric potential distributions in the waterlogged banks of Giber Å demonstrated the presence of distant electric redox coupling in naturally occurring freshwater sediment. At the same site, filamentous Desulfobulbaceae with cable bacterium morphology were found to be present. Their 16S rRNA gene sequence placed them as a distinct sister group to the known marine cable bacteria, with the genus Desulfobulbus as the closest cultured lineage. The results of the present study indicate that electric currents mediated by cable bacteria could be important for the biogeochemistry in many more environments than anticipated thus far and suggest a common evolutionary origin of the cable phenotype within Desulfobulbaceae with subsequent diversification into a freshwater and a marine lineage. PMID:26116678

  19. Cable Bacteria in Freshwater Sediments

    PubMed Central

    Kristiansen, Michael; Frederiksen, Rasmus B.; Dittmer, Anders Lindequist; Bjerg, Jesper Tataru; Trojan, Daniela; Schreiber, Lars; Damgaard, Lars Riis; Schramm, Andreas; Nielsen, Lars Peter

    2015-01-01

    In marine sediments cathodic oxygen reduction at the sediment surface can be coupled to anodic sulfide oxidation in deeper anoxic layers through electrical currents mediated by filamentous, multicellular bacteria of the Desulfobulbaceae family, the so-called cable bacteria. Until now, cable bacteria have only been reported from marine environments. In this study, we demonstrate that cable bacteria also occur in freshwater sediments. In a first step, homogenized sediment collected from the freshwater stream Giber , Denmark, was incubated in the laboratory. After 2 weeks, pH signatures and electric fields indicated electron transfer between vertically separated anodic and cathodic half-reactions. Fluorescence in situ hybridization revealed the presence of Desulfobulbaceae filaments. In addition, in situ measurements of oxygen, pH, and electric potential distributions in the waterlogged banks of Giber demonstrated the presence of distant electric redox coupling in naturally occurring freshwater sediment. At the same site, filamentous Desulfobulbaceae with cable bacterium morphology were found to be present. Their 16S rRNA gene sequence placed them as a distinct sister group to the known marine cable bacteria, with the genus Desulfobulbus as the closest cultured lineage. The results of the present study indicate that electric currents mediated by cable bacteria could be important for the biogeochemistry in many more environments than anticipated thus far and suggest a common evolutionary origin of the cable phenotype within Desulfobulbaceae with subsequent diversification into a freshwater and a marine lineage. PMID:26116678

  20. Empirical and mechanistic models for the particle export ratio

    NASA Astrophysics Data System (ADS)

    Dunne, John P.; Armstrong, Robert A.; Gnanadesikan, Anand; Sarmiento, Jorge L.

    2005-12-01

    We present new empirical and mechanistic models for predicting the export of organic carbon out of the surface ocean by sinking particles. To calibrate these models, we have compiled a synthesis of field observations related to ecosystem size structure, primary production and particle export from around the globe. The empirical model captures 61% of the observed variance in the ratio of particle export to primary production (the pe ratio) using sea-surface temperature and chlorophyll concentrations (or primary productivity) as predictor variables. To describe the mechanisms responsible for pe-ratio variability, we present size-based formulations of phytoplankton grazing and sinking particle export, combining them into an alternative, mechanistic model. The formulation of grazing dynamics, using simple power laws as closure terms for small and large phytoplankton, reproduces 74% of the observed variability in phytoplankton community composition wherein large phytoplankton augment small ones as production increases. The formulation for sinking particle export partitions a temperature-dependent fraction of small and large phytoplankton grazing into sinking detritus. The mechanistic model also captures 61% of the observed variance in pe ratio, with large phytoplankton in high biomass and relatively cold regions leading to more efficient export. In this model, variability in primary productivity results in a biomass-modulated switch between small and large phytoplankton pathways.

  1. Detection and variability of the Congo River plume from satellite derived sea surface temperature, salinity, ocean colour and sea level

    NASA Astrophysics Data System (ADS)

    Hopkins, Jo; Lucas, Marc; Dufau, Claire; Sutton, Marion; Lauret, Olivier

    2013-04-01

    The Congo River in Africa has the world's second highest annual mean daily freshwater discharge and is the second largest exporter of terrestrial organic carbon into the oceans. It annually discharges an average of 1,250 109 m3 of freshwater into the southeast Atlantic producing a vast fresh water plume, whose signature can be traced hundreds of kilometres from the river mouth. Large river plumes such as this play important roles in the ocean carbon cycle, often functioning as carbon sinks. An understanding of their extent and seasonality is therefore essential if they are to be realistically accounted for in global assessments of the carbon cycle. Despite its size, the variability and dynamics of the Congo plume are minimally documented. In this paper we analyse satellite derived sea surface temperature, salinity, ocean colour and sea level anomaly to describe and quantify the extent, strength and variability of the far-field plume and to explain its behaviour in relation to winds, ocean currents and fresh water discharge. Empirical Orthogonal Function analysis reveals strong seasonal and coastal upwelling signals, potential bimodal seasonality of the Angola Current and responses to fresh water discharge peaks in all data sets. The strongest plume-like signatures however were found in the salinity and ocean colour where the dominant sources of variability come from the Congo River itself, rather than from the wider atmosphere and ocean. These two data sets are then analysed using a statistically based water mass detection technique to isolate the behaviour of the plume. The Congo's close proximity to the equator means that the influence of the earth's rotation on the fresh water inflow is relatively small and the plume tends not to form a distinct coastal current. Instead, its behaviour is determined by wind and surface circulation patterns. The main axis of the plume between November and February, following peak river discharge, is oriented northwest, driven by the wind and Ekman surface currents and possibly a northern branch of the Benguela Coastal Current. From February through to May the main axis swings towards the southwest, extending 750 km from the mouth, coinciding with a westerly shift in the wind direction and an increase in its speed. From June through to August, when discharge is at a minimum and the plumes salinity is highest, the main axis of the plume extends up to 850 km westward, but retreats to 440 km throughout the autumn. Following the end of the coastal upwelling period and an increase in river discharge the plumes salinity starts to rise again and the equatorward fresh water tongue re-establishes itself.

  2. Effects of acidification on olfactory-mediated behaviour in freshwater and marine ecosystems: a synthesis

    PubMed Central

    Leduc, Antoine O. H. C.; Munday, Philip L.; Brown, Grant E.; Ferrari, Maud C. O.

    2013-01-01

    For many aquatic organisms, olfactory-mediated behaviour is essential to the maintenance of numerous fitness-enhancing activities, including foraging, reproduction and predator avoidance. Studies in both freshwater and marine ecosystems have demonstrated significant impacts of anthropogenic acidification on olfactory abilities of fish and macroinvertebrates, leading to impaired behavioural responses, with potentially far-reaching consequences to population dynamics and community structure. Whereas the ecological impacts of impaired olfactory-mediated behaviour may be similar between freshwater and marine ecosystems, the underlying mechanisms are quite distinct. In acidified freshwater, molecular change to chemical cues along with reduced olfaction sensitivity appear to be the primary causes of olfactory-mediated behavioural impairment. By contrast, experiments simulating future ocean acidification suggest that interference of high CO2 with brain neurotransmitter function is the primary cause for olfactory-mediated behavioural impairment in fish. Different physico-chemical characteristics between marine and freshwater systems are probably responsible for these distinct mechanisms of impairment, which, under globally rising CO2 levels, may lead to strikingly different consequences to olfaction. While fluctuations in pH may occur in both freshwater and marine ecosystems, marine habitat will remain alkaline despite future ocean acidification caused by globally rising CO2 levels. In this synthesis, we argue that ecosystem-specific mechanisms affecting olfaction need to be considered for effective management and conservation practices. PMID:23980246

  3. Effects of acidification on olfactory-mediated behaviour in freshwater and marine ecosystems: a synthesis.

    PubMed

    Leduc, Antoine O H C; Munday, Philip L; Brown, Grant E; Ferrari, Maud C O

    2013-01-01

    For many aquatic organisms, olfactory-mediated behaviour is essential to the maintenance of numerous fitness-enhancing activities, including foraging, reproduction and predator avoidance. Studies in both freshwater and marine ecosystems have demonstrated significant impacts of anthropogenic acidification on olfactory abilities of fish and macroinvertebrates, leading to impaired behavioural responses, with potentially far-reaching consequences to population dynamics and community structure. Whereas the ecological impacts of impaired olfactory-mediated behaviour may be similar between freshwater and marine ecosystems, the underlying mechanisms are quite distinct. In acidified freshwater, molecular change to chemical cues along with reduced olfaction sensitivity appear to be the primary causes of olfactory-mediated behavioural impairment. By contrast, experiments simulating future ocean acidification suggest that interference of high CO2 with brain neurotransmitter function is the primary cause for olfactory-mediated behavioural impairment in fish. Different physico-chemical characteristics between marine and freshwater systems are probably responsible for these distinct mechanisms of impairment, which, under globally rising CO2 levels, may lead to strikingly different consequences to olfaction. While fluctuations in pH may occur in both freshwater and marine ecosystems, marine habitat will remain alkaline despite future ocean acidification caused by globally rising CO2 levels. In this synthesis, we argue that ecosystem-specific mechanisms affecting olfaction need to be considered for effective management and conservation practices. PMID:23980246

  4. Meltwater Events in the Eastern Arctic Ocean: Relations to Eurasian Ice-dammed Lakes and Climate Forcings

    NASA Astrophysics Data System (ADS)

    Spielhagen, R. F.

    2005-12-01

    Analysis of foraminiferal oxygen and carbon isotope records from long sediment cores from the eastern and central Arctic Ocean reveals a number of peaks which are interpreted as evidence for strong meltwater events. Most of these events were accompanied by strong deposition of coarse ice-rafted terrestrial debris indicative of large amounts of icebergs in the area. Hgh-resolution stratigraphic models for the cores, based on a variety of independant methods, allow to identify the the ages of meltwater events within the last 200 ky. They cluster in the intervals 160-155, 140-125, 90-75, 65-60, and 55-50 ka. According to recent results from the QUEEN program (Quaternary Science Reviews, v. 23 (11-13), 2004), these times fall into intervals of extended glaciations in northern Eurasia. The ice sheets dammed large rivers in European Russia and western Siberia and led to the formation of large lakes. The "marine" ages of meltwater events in the Arctic Ocean, as determined from sediment core data, correlate well with terrestrial age estimates for the deglacial events in northern Eurasia which must have included the discharge of the meltwater lakes into the Arctic Ocean. According to amplitudes in the foraminiferal isotopic records, the strongest events occurred at the glacial terminations of marine isotope stages 6 (130 ka) and 3/4 (52 ka). In my presentation, I will give an overview of existing stratigraphic and isotopic data sets of meltwater events in the eastern and central Arctic Ocean, including their limitations. Furthermore, I will analyze possible connections of meltwater events in the Arctic to similar events in the Norwegian-Greenland Sea and to external forcings. Finally, possible evidence for a strong freshwater export from the Arctic Ocean as a trigger of the cold Younger Dryas event will be reviewed.

  5. Ocean tides

    NASA Technical Reports Server (NTRS)

    Hendershott, M. C.

    1975-01-01

    A review of recent developments in the study of ocean tides and related phenomena is presented. Topics briefly discussed include: the mechanism by which tidal dissipation occurs; continental shelf, marginal sea, and baroclinic tides; estimation of the amount of energy stored in the tide; the distribution of energy over the ocean; the resonant frequencies and Q factors of oceanic normal modes; the relationship of earth tides and ocean tides; and numerical global tidal models.

  6. Freshwater outburst from Lake Superior as a trigger for the cold event 9300 years ago.

    PubMed

    Yu, Shi-Yong; Colman, Steven M; Lowell, Thomas V; Milne, Glenn A; Fisher, Timothy G; Breckenridge, Andy; Boyd, Matthew; Teller, James T

    2010-06-01

    Paleoclimate proxy records reveal a pervasive cooling event with a Northern Hemispheric extent approximately 9300 years ago. Coeval changes in the oceanic circulation of the North Atlantic imply freshwater forcing. However, the source, magnitude, and routing of meltwater have remained unknown. Located in central North America, Lake Superior is a key site for regulating the outflow of glacial meltwater to the oceans. Here, we show evidence for an approximately 45-meter rapid lake-level fall in this basin, centered on 9300 calibrated years before the present, due to the failure of a glacial drift dam on the southeast corner of the lake. We ascribe the widespread climate anomaly approximately 9300 years ago to this freshwater outburst delivered to the North Atlantic Ocean through the Lake Huron-North Bay-Ottawa River-St. Lawrence River valleys. PMID:20430972

  7. An electromagnetic geophysical survey of the freshwater lens of Isla de Mona, Puerto Rico

    USGS Publications Warehouse

    Richards, R.T.; Troester, J.W.; Martinez, M.I.

    1998-01-01

    An electromagnetic reconnaissance of the freshwater lens of Isla de Mona, Puerto Rico was conducted with both terrain conductivity (TC) and transient electromagnetic (TEM) surface geophysical techniques. These geophysical surveys were limited to the southern and western parts of the island because of problems with access and cultural metallic objects such as reinforced concrete roadways on the eastern part of the island. The geophysical data were supplemented with the location of a freshwater spring found by scuba divers at a depth of about 20 m below sea level along the northern coast of the island. The geophysical data suggest that the freshwater lens has a maximum thickness of 20 m in the southern half of the island. The freshwater lens is not thickest at the center of the island but nearer the southwestern edge in Quaternary deposits and the eastern edge of the island in the Tertiary carbonates. This finding indicates that the groundwater flow paths on Isla de Mona are not radially summetrical from the center of the island to the ocean. The asymmetry of the freshwater lens indicates that the differences in hydraulic conductivity are a major factor in determining the shape of the freshwater lens. The porosity of the aquifer, as determined by the geophysical data is about 33%.

  8. Productivity and salinity structuring of the microplankton revealed by comparative freshwater metagenomics

    PubMed Central

    Eiler, Alexander; Zaremba-Niedzwiedzka, Katarzyna; Martínez-García, Manuel; McMahon, Katherine D; Stepanauskas, Ramunas; Andersson, Siv G E; Bertilsson, Stefan

    2014-01-01

    Little is known about the diversity and structuring of freshwater microbial communities beyond the patterns revealed by tracing their distribution in the landscape with common taxonomic markers such as the ribosomal RNA. To address this gap in knowledge, metagenomes from temperate lakes were compared to selected marine metagenomes. Taxonomic analyses of rRNA genes in these freshwater metagenomes confirm the previously reported dominance of a limited subset of uncultured lineages of freshwater bacteria, whereas Archaea were rare. Diversification into marine and freshwater microbial lineages was also reflected in phylogenies of functional genes, and there were also significant differences in functional beta-diversity. The pathways and functions that accounted for these differences are involved in osmoregulation, active transport, carbohydrate and amino acid metabolism. Moreover, predicted genes orthologous to active transporters and recalcitrant organic matter degradation were more common in microbial genomes from oligotrophic versus eutrophic lakes. This comparative metagenomic analysis allowed us to formulate a general hypothesis that oceanic- compared with freshwater-dwelling microorganisms, invest more in metabolism of amino acids and that strategies of carbohydrate metabolism differ significantly between marine and freshwater microbial communities. PMID:24118837

  9. Freshwater from the Bay of Biscay shelves in 2009

    NASA Astrophysics Data System (ADS)

    Reverdin, G.; Marié, L.; Lazure, P.; d'Ovidio, F.; Boutin, J.; Testor, P.; Martin, N.; Lourenco, A.; Gaillard, F.; Lavin, A.; Rodriguez, C.; Somavilla, R.; Mader, J.; Rubio, A.; Blouch, P.; Rolland, J.; Bozec, Y.; Charria, G.; Batifoulier, F.; Dumas, F.; Louazel, S.; Chanut, J.

    2013-01-01

    In April-November 2009, surface salinity data provide a good coverage of most of the south-east Bay of Biscay and nearby Aquitaine/Armorican shelves. By late April most of the shelf, in particular south of 46°N, is covered by a fresh surface layer amounting to a fresh water volume of 49 · 109 m3. At that time, a moderate amount of fresh water has spread over the Landes Plateau. By mid-June, this shelf water penetrates over the Cape Ferret Canyon north of the Landes Plateau. By mid-July, it is found west of the Landes Plateau to at least 4°W, with an estimated fresh-water content of 11-14 · 109 m3. Drifters deployed on June 17 in the Cape Ferret Canyon, or later on the shelves, confirm the spreading of shelf fresh-water over the deep ocean. Lagrangian tracking using altimetric products, also confirms the transport by a quasi-stationary circulation. Operational numerical simulations (PREVIMER, IBI, HYCOM) display this spread of the freshwater, but in different areas. In particular, all have some fresh water escaping westward near the coast in the Basque region, which is not observed. Later in the summer season, the fresh water spreads westward to south-westward and along the shelf break to at least 5.5°W in late September.

  10. Black Carbon in Estuarine and Coastal Ocean Dissolved Organic Matter

    NASA Technical Reports Server (NTRS)

    Mannino, Antonio; Harvey, H. Rodger

    2003-01-01

    Analysis of high-molecular-weight dissolved organic matter (DOM) from two estuaries in the northwest Atlantic Ocean reveals that black carbon (BC) is a significant component of previously uncharacterized DOM, suggesting that river-estuary systems are important exporters of recalcitrant dissolved organic carbon to the ocean.

  11. Arctic circulation regimes and Greenland freshwater in the sub-Arctic seas

    NASA Astrophysics Data System (ADS)

    Dukhovskoy, Dmitry; Proshutinsky, Andrey; Herbaut, Christophe; Aksenov, Yevgeny; Luneva, Maria; Myers, Paul; Platov, Gennady; Popova, Ekaterina

    2015-04-01

    Between 1948 and 1996, wind-driven components of ice drift and surface ocean currents experienced a well pronounced decadal variability alternating between anticyclonic and cyclonic circulation regimes. During cyclonic regimes, low sea level atmospheric pressure dominated over the Arctic Ocean driving sea ice and the upper ocean clockwise; the Arctic atmosphere was relatively warm and humid and freshwater flux from the Arctic Ocean toward the sub-Arctic seas was intensified. During anticylonic circulation regimes, high sea level pressure dominated over the Arctic driving sea ice and ocean counter-clockwise; the atmosphere was cold and dry and the freshwater flux from the Arctic to the sub-Arctic seas was reduced. Since 1997, however, the Arctic system has been dominated by a 17-year anticyclonic circulation regime with a set of environmental parameters that are atypical for these regimes. Of essential importance is to discern the causes and consequences of the apparent break-down in the natural decadal variability of the Arctic climate system, and specifically: Why has the well-pronounced decadal variability observed in the 20th century been replaced by relatively weak interannual changes under anticyclonic circulation regime conditions in the 21st century? We speculate that before the 2000s, the freshwater and heat exchanges between the Arctic Ocean and the North Atlantic were self-regulated and their interactions were realized via decadal climate oscillations. In the 21st century, this near-decadal variability has been interrupted as a result of an additional freshwater source associated with Greenland ice sheet melt. We hypothesize that the excess freshwater flux from Greenland has reduced deep convection in the sub-Arctic seas, resulting in the cessation of decadal oscillations in Arctic climate regimes. In order to test this hypothesis, numerical experiments with a set of FAMOS (Forum for Arctic Modeling & Observational Synthesis) ice-ocean coupled models have been conducted. In these experiments, Greenland freshwater is tracked by passive tracers being constantly released along the Greenland coast. The experiments demonstrate propagation pathways and time scales of freshening signal within the sub-Arctic seas.

  12. The effect of Congo River freshwater discharge on Eastern Equatorial Atlantic climate variability

    NASA Astrophysics Data System (ADS)

    Materia, Stefano; Gualdi, Silvio; Navarra, Antonio; Terray, Laurent

    2012-11-01

    The surface ocean explains a considerable part of the inter-annual Tropical Atlantic variability. The present work makes use of observational datasets to investigate the effect of freshwater flow on sea surface salinity (SSS) and temperature (SST) in the Gulf of Guinea. In particular, the Congo River discharges a huge amount of freshwater into the ocean, affecting SSS in the Eastern Equatorial Atlantic (EEA) and stratifying the surface layers. The hypothesis is that an excess of river runoff emphasize stratification, influencing the ocean temperature. In fact, our findings show that SSTs in the Gulf of Guinea are warmer in summers following an anomalously high Congo spring discharge. Vice versa, when the river discharges low freshwater, a cold anomaly appears in the Gulf. The response of SST is not linear: temperature anomalies are considerable and long-lasting in the event of large freshwater flow, while in dry years they are less remarkable, although still significant. An excess of freshwater seems able to form a barrier layer, which inhibits vertical mixing and the entrainment of the cold thermocline water into the surface. Other processes may contribute to SST variability, among which the net input of atmospheric freshwater falling over EEA. Likewise the case of continental runoff from Congo River, warm anomalies occur after anomalously rainy seasons and low temperatures follow dry seasons, confirming the effect of freshwater on SST. However, the two sources of freshwater anomaly are not in phase, so that it is possible to split between atypical SST following continental freshwater anomalies and rainfall anomalies. Also, variations in air-sea fluxes can produce heating and cooling of the Gulf of Guinea. Nevertheless, atypical SSTs cannot be ascribed to fluxes, since the temperature variation induced by them is not sufficient to explain the SST anomalies appearing in the Gulf after anomalous peak discharges. The interaction processes between river runoff, sea surface salinity and temperature play an effective role in the interannual variability in the EEA region. Our results add a new source of variability in the area, which was often neglected by previous studies.

  13. Arctic Freshwater Distribution and the Arctic Oscillation: comparison of results from complex and simple models.

    NASA Astrophysics Data System (ADS)

    Newton, R.; Cane, M.; Schlosser, P.

    2002-05-01

    A high-resolution ice-ocean general circulation model is used to study recent changes in the distribution of freshwater in the Arctic. The results are presented, and are compared with the results of a (much) simpler model of the large-scale, long-term impact of annular forcing on the Arctic. It is argued that the results of the general circulation model are consistent with both the simple dynamical calculation and recent observations. Conclusions are drawn about both the mean state of the freshwater reservoir in the Arctic, and its interannual to decade-scale variations.

  14. Biomass production by freshwater and marine macrophytes

    SciTech Connect

    North, W.J.; Gerard, V.A.; Kuwabara, J.S.

    1981-01-01

    Research on aquatic macrophytes as producers of biomass has been undertaken at Woods Hole Oceanographic Institution (WHOI) on the east coast and on the west coast by a group of collaborators in a joint effort known as the Marine Biomass Project. Studies at WHOI have focused on estuarine and coastal situations with some attention recently to freshwater plants. The Marine Farm Project has primarily been concerned with oceanic biomass production. A group at WHOI has undertaken a wide variety of studies concerning aquatic macrophytes including nutrient uptake, growth, yields, and environmental factors affecting yields. Aquatic biomass production systems have been surveyed on a worldwide basis and currently the role of carbon as a potential limiting nutrient in biomass culturing is being examined. The Marine Farm Project is presently attempting to grow giant kelp in offshore waters off southern California. Other work related to aquatic biomass production includes an investigation at the University of California, Berkeley, of microalgae in ponds. This paper will emphasize discussion of the kelp production phases of the Marine Farm Project. Activities by the WHOI are briefly summarized.

  15. The Arctic Ocean Perennial Ice Zone

    NASA Technical Reports Server (NTRS)

    Kwok, R.; Cunningham, G. F.; Yueh, S.

    1998-01-01

    This study shows that: 1) the NSCAT backscatter fields provide an estimate of the PIZ coverage of the Arctic Ocean; and, 2) the decrease in PIZ area over the winter gives an indication of the PIZ area exported through Fram Strait.

  16. Water quality for freshwater fish

    SciTech Connect

    Howells, G. )

    1994-01-01

    This timely and up-to-date volume brings together recent critical reviews on water quality requirements for freshwater fish commissioned by the European Inland Fisheries Advisory Commission, an agency of the United Nations Food and Agriculture Organization. It provides a unique and authoritative source of critically evaluated water quality data concerning the effects of chromium, nickel, aluminum and nitrite on freshwater fish and includes an assessment of the toxicity of mixtures. The reports presented in this volume cover all stages of the life cycle and relevant trophic levels, including aquatic invertebrates and plants and potential bioaccumulation through the food chain. An extensive bibliography is provided for each chapter as well as a glossary of terms and a list of fish species mentioned in the text. This compilation of papers is the definitive reference volume for chemists, biologists, ecologists and toxicologists as well as for water resource managers concerned with management and control of pollution in fresh waters.

  17. Forcing, variability, and pathway of a freshwater-driven current in the Eurasian Arctic

    NASA Astrophysics Data System (ADS)

    Janout, Markus; Aksenov, Yevgeny; Hlemann, Jens; Rabe, Benjamin; Schauer, Ursula; Polyakov, Igor; Bacon, Sheldon; Coward, Andrew; Karcher, Michael; Lenn, Yueng-Djern; Kassens, Heidi; Timokhov, Leo

    2015-04-01

    Siberian river water is a first-order contribution to the Arctic freshwater budget, with the Ob, Yenisey, and Lena supplying nearly half of the total surface freshwater flux. However, few details are known regarding where, when and how the freshwater transverses the vast Siberian shelf seas. This paper investigates the mechanism, variability and pathways of the fresh Kara Sea outflow through Vilkitsky Strait towards the Laptev Sea. We utilize a high-resolution ocean model and recent shipboard observations to characterize the freshwater-laden Vilkitsky Strait Current (VSC), and shed new light on the little-studied region between the Kara and Laptev Seas, characterized by harsh ice conditions, contrasting water masses, straits and a large submarine canyon. The VSC is 10-20 km wide, surface-intensified, and varies seasonally (maximum from August-March) and interannually. Average freshwater (volume) transport is 500 120 km3 a-1 (0.53 0.08 Sv), with a baroclinic flow contribution of 50-90%. Interannual transport variability is explained by a storage-release mechanism, where blocking-favorable summer winds hamper the outflow and cause accumulation of freshwater in the Kara Sea. The year following a blocking event is characterized by enhanced transports driven by a baroclinic flow along the coast that is set up by increased freshwater volumes. Eventually, the VSC merges with a slope current and provides a major pathway for Eurasian river water towards the Western Arctic along the Eurasian continental slope. Kara (and Laptev) Sea freshwater transport is not correlated with the Arctic Oscillation, but rather driven by regional summer pressure patterns.

  18. A synthesis of upper ocean carbon and dissolved iron budgets for Southern Ocean natural iron fertilisation studies

    NASA Astrophysics Data System (ADS)

    Morris, Paul J.; Charette, Matthew A.

    2013-06-01

    For over a decade the relationship between iron addition and carbon export has been an active topic of Southern Ocean biogeochemical investigation. To study the iron-carbon interaction, a number of natural iron sources within the Antarctic Circumpolar Current have been targeted to quantify the resultant particulate organic carbon (POC) export. Three studies in particular near the Crozet Islands, Kerguelen Plateau, and Antarctic Peninsula have produced estimates of both dissolved iron (DFe) supply and POC export. For each area, we present a detailed synthesis of 234Thorium-derived POC export and of the DFe budgets that fuel the substantial phytoplankton blooms observed in these areas. Furthermore, we discuss the nuances of calculating seasonal POC export, which is required to estimate the seasonal response of POC export to DFe fertilisation. To conclude, we review the relationship between DFe supply and POC export (C:Fe ratio) for these areas, which provides an estimate of POC export efficiency. Daily rates of POC export from the mixed layer of naturally Fe-enriched Southern Ocean blooms range from 15 to 32 mmol C m-2 d-1, with associated control sites typically exporting 3-times less POC, (5 to 12 mmol C m-2 d-1). Within each project, the 3-fold trend is also observed in estimates of seasonal POC export; however, variation between study regions shows up to a 4-fold difference (range 1.4-5.0 mol m-2). DFe supply is dominated by horizontal processes and spans an order of magnitude depending on the location (190-2700 nmol m-2 d-1). Where the calculation of seasonal C:Fe ratios is possible, almost an order of magnitude variation (16,790-154,000) is observed between different Southern Ocean regions.

  19. Influence of net freshwater supply on salinity in Florida Bay

    NASA Astrophysics Data System (ADS)

    Nuttle, William K.; Fourqurean, James W.; Cosby, Bernard J.; Zieman, Joseph C.; Robblee, Michael B.

    2000-07-01

    An annual water budget for Florida Bay, the large, seasonally hypersaline estuary in the Everglades National Park, was constructed using physically based models and long-term (31 years) data on salinity, hydrology, and climate. Effects of seasonal and interannual variations of the net freshwater supply (runoff plus rainfall minus evaporation) on salinity variation within the bay were also examined. Particular attention was paid to the effects of runoff, which are the focus of ambitious plans to restore and conserve the Florida Bay ecosystem. From 1965 to 1995 the annual runoff from the Everglades into the bay was less than one tenth of the annual direct rainfall onto the bay, while estimated annual evaporation slightly exceeded annual rainfall. The average net freshwater supply to the bay over a year was thus approximately zero, and interannual variations in salinity appeared to be affected primarily by interannual fluctuations in rainfall. At the annual scale, runoff apparently had little effect on the bay as a whole during this period. On a seasonal basis, variations in rainfall, evaporation, and runoff were not in phase, and the net freshwater supply to the bay varied between positive and negative values, contributing to a strong seasonal pattern in salinity, especially in regions of the bay relatively isolated from exchanges with the Gulf of Mexico and Atlantic Ocean. Changes in runoff could have a greater effect on salinity in the bay if the seasonal patterns of rainfall and evaporation and the timing of the runoff are considered. One model was also used to simulate spatial and temporal patterns of salinity responses expected to result from changes in net freshwater supply. Simulations in which runoff was increased by a factor of 2 (but with no change in spatial pattern) indicated that increased runoff will lower salinity values in eastern Florida Bay, increase the variability of salinity in the South Region, but have little effect on salinity in the Central and West Regions.

  20. Influence of net freshwater supply on salinity in Florida Bay

    USGS Publications Warehouse

    Nuttle, W.K.; Fourqurean, J.W.; Cosby, B.J.; Zieman, J.C.; Robblee, M.B.

    2000-01-01

    An annual water budget for Florida Bay, the large, seasonally hypersaline estuary in the Everglades National Park, was constructed using physically based models and long-term (31 years) data on salinity, hydrology, and climate. Effects of seasonal and interannual variations of the net freshwater supply (runoff plus rainfall minus evaporation) on salinity variation within the bay were also examined. Particular attention was paid to the effects of runoff, which are the focus of ambitious plans to restore and conserve the Florida Bay ecosystem. From 1965 to 1995 the annual runoff from the Everglades into the bay was less than one tenth of the annual direct rainfall onto the bay, while estimated annual evaporation slightly exceeded annual rainfall. The average net freshwater supply to the bay over a year was thus approximately zero, and interannual variations in salinity appeared to be affected primarily by interannual fluctuations in rainfall. At the annual scale, runoff apparently had little effect on the bay as a whole during this period. On a seasonal basis, variations in rainfall, evaporation, and runoff were not in phase, and the net freshwater supply to the bay varied between positive and negative values, contributing to a strong seasonal pattern in salinity, especially in regions of the bay relatively isolated from exchanges with the Gulf of Mexico and Atlantic Ocean. Changes in runoff could have a greater effect on salinity in the bay if the seasonal patterns of rainfall and evaporation and the timing of the runoff are considered. One model was also used to simulate spatial and temporal patterns of salinity responses expected to result from changes in net freshwater supply. Simulations in which runoff was increased by a factor of 2 (but with no change in spatial pattern) indicated that increased runoff will lower salinity values in eastern Florida Bay, increase the variability of salinity in the South Region, but have little effect on salinity in the Central and West Regions.

  1. Freshwater exhange in the Sunda Strait estimated by Aquarius

    NASA Astrophysics Data System (ADS)

    Potemra, J. T.; Hacker, P. W.; Maximenko, N. A.; Melnichenko, O.

    2012-12-01

    The Pacific and Indian Oceans are connected at a low latitude via the Indonesian Throughflow (ITF). Through direct observations it is now understood that approximately 10 to 15 Sv of water are transported from the Pacific to the Indian Ocean. The implications of this transport, including impacts to water mass formation, heat and freshwater budgets and potential feedbacks to the atmosphere are still under investigation. One of the complexities in this region is the large number of smaller straits and passages between islands that may or may not play an important role in ITF processes. Many of these straits are more narrow than the typical resolution of ocean circulation models, and therefore are not properly simulated. For mass transport this is likely not an issue, since recent observations suggest that most of the mass transport flows via the Makassar Strait and then exits to the Indian Ocean via the Lombok, Ombai and Timor passages. This study, however, focuses on the fresh water transport between the Indonesian Seas and the Indian Ocean in particular via the Sunda Strait. There are very few direct observations of the upper ocean stratification in this region. Conversely, the recent launch of the Aquarius mission provides a unique opportunity to study the transport of fresh water, as indicated by sea surface salinity variability, between the Java Sea and the eastern Indian Ocean. Numerical model results, Argo measurements and Aquarius-derived sea surface salinity are used to examine the annual variability of fresh water exchange via the Sunda Strait. Model mass transport is typically low, averaging less than 1 Sv, but fresh water transport could have important implications for stratification along the Sumatra/Java southern coast and thus impact coastal wave propagation. The satellite derived sea surface salinity will be used to show the importance of seasonal variations in this region.

  2. Robotic observations of enhanced carbon biomass and export at 55 degrees during SOFeX.

    PubMed

    Bishop, James K B; Wood, Todd J; Davis, Russ E; Sherman, Jeffrey T

    2004-04-16

    Autonomous floats profiling in high-nitrate low-silicate waters of the Southern Ocean observed carbon biomass variability and carbon exported to depths of 100 m during the 2002 Southern Ocean Iron Experiment (SOFeX) to detect the effects of iron fertilization of surface water there. Control and "in-patch" measurements documented a greater than fourfold enhancement of carbon biomass in the iron-amended waters. Carbon export through 100 m increased two- to sixfold as the patch subducted below a front. The molar ratio of iron added to carbon exported ranged between 10(4) and 10(5). The biomass buildup and export were much higher than expected for iron-amended low-silicate waters. PMID:15087544

  3. Bubble size distribution under saltwater and freshwater breaking waves

    NASA Astrophysics Data System (ADS)

    Cartmill, John W.; Yang Su, Ming

    1993-11-01

    The chemical composition of salt water profoundly alters the process of microbubble formation and must be accounted for in extrapolating freshwater results to the ocean environment. Results are presented of the measurement of bubble size distributions generated by breaking waves in both freshwater and saltwater laboratory tanks. Bubble radii in the range of 34-1200 ? m were measured by an acoustic resonator at various positions and depths in a large-scale wave tank at Oregon State University. This experiment represents the first attempt to measure bubbles produced by breaking waves at this large scale in a saltwater tank. Mechanically generated wave groups, with maximum wave height of 4 ft, were used to produce breaking waves and bubble plumes comparable in scale with moderate ocean waves. During the experiment salt was added to bring the salinity of the water to 30%. This salinity alters the nature of the bubbles produced and their subsequent evolution. An order of magnitude increase in the number density over the entire size range was observed for salt water vs. fresh water.

  4. 78 FR 37518 - Order Denying Export Privileges

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-21

    ... Bureau of Industry and Security Order Denying Export Privileges In the Matter of: Lee Roy Perez, Inmate... convicted of violating Section 38 of the Arms Export Control Act (22 U.S.C. 2778 (2006 & Supp. IV 2010... exported and attempting to export and attempting to cause to be exported from the United States to...

  5. 19 CFR 10.430 - Export requirements.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 19 Customs Duties 1 2011-04-01 2011-04-01 false Export requirements. 10.430 Section 10.430 Customs... Export Requirements 10.430 Export requirements. (a) Submission of certification to CBP. An exporter or producer in the United States that signs a certification of origin for a good exported from the...

  6. The Microbiota of Freshwater Fish and Freshwater Niches Contain Omega-3 Fatty Acid-Producing Shewanella Species.

    PubMed

    Dailey, Frank E; McGraw, Joseph E; Jensen, Brittany J; Bishop, Sydney S; Lokken, James P; Dorff, Kellen J; Ripley, Michael P; Munro, James B

    2015-01-01

    Approximately 30 years ago, it was discovered that free-living bacteria isolated from cold ocean depths could produce polyunsaturated fatty acids (PUFA) such as eicosapentaenoic acid (EPA) (20:5n-3) or docosahexaenoic acid (DHA) (22:6n-3), two PUFA essential for human health. Numerous laboratories have also discovered that EPA- and/or DHA-producing bacteria, many of them members of the Shewanella genus, could be isolated from the intestinal tracts of omega-3 fatty acid-rich marine fish. If bacteria contribute omega-3 fatty acids to the host fish in general or if they assist some bacterial species in adaptation to cold, then cold freshwater fish or habitats should also harbor these producers. Thus, we undertook a study to see if these niches also contained omega-3 fatty acid producers. We were successful in isolating and characterizing unique EPA-producing strains of Shewanella from three strictly freshwater native fish species, i.e., lake whitefish (Coregonus clupeaformis), lean lake trout (Salvelinus namaycush), and walleye (Sander vitreus), and from two other freshwater nonnative fish, i.e., coho salmon (Oncorhynchus kisutch) and seeforellen brown trout (Salmo trutta). We were also able to isolate four unique free-living strains of EPA-producing Shewanella from freshwater habitats. Phylogenetic and phenotypic analyses suggest that one producer is clearly a member of the Shewanella morhuae species and another is sister to members of the marine PUFA-producing Shewanella baltica species. However, the remaining isolates have more ambiguous relationships, sharing a common ancestor with non-PUFA-producing Shewanella putrefaciens isolates rather than marine S. baltica isolates despite having a phenotype more consistent with S. baltica strains. PMID:26497452

  7. Upper Ocean Variability in the Indo-Pacific Warm Pool during the Late Holocene, Early Holocene and Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Xu, J.; Kuhnt, W.; Holbourn, A. E.; Andersen, N.

    2009-12-01

    We analyzed oxygen isotopes and Mg/Ca ratios in the surface dwelling planktonic foraminifer Globigerinoides ruber (white s.s.) and the thermocline dweller Pulleniatina obliquiloculata to improve understanding of upper ocean spatial variability in the Indo-Pacific Warm Pool (IPWP). We focused on three critical time intervals: the Last Glacial Maximum (LGM; 18-21.5 ka), the early Holocene (8-9 ka) and the late Holocene (0-2 ka). Our records from twenty-four stations in the South China Sea, Timor Sea, Indonesian seas and western Pacific indicate overall dry and cool conditions in the IPWP during the LGM with a low thermal gradient between surface and thermocline waters. Warm surface waters (>28 Celsius degree) spread over the entire region during the early Holocene, indicating substantial expansion of the IPWP. However in the eastern Indian Ocean (Timor Sea), the thermocline gradually shoaled from the LGM to early Holocene, reflecting intensification of the subsurface Indonesian Throughflow. Increased precipitation over the South China Sea appears related to an intensified summer monsoon and northward displacement of the Intertropical Convergence Zone. Increased freshwater export from the South China Sea through the Java Sea also contributed to a change in the vertical structure of the Indonesian Throughflow from surface- to thermocline-dominated flow and a freshening of Timor Sea waters during the early Holocene.

  8. Climatological monthly heat and freshwater flux estimates on a global scale from Argo

    NASA Astrophysics Data System (ADS)

    Giglio, Donata; Roemmich, Dean

    2014-10-01

    The global pattern of climatological monthly heat and freshwater fluxes at the ocean surface is estimated using Argo temperature and salinity profile data for the period 2004-2013. Temperature or salinity changes are calculated in a volume of water above an isopycnal that is below the mixed layer and not subject to mixed-layer entrainment. Horizontal advection components from geostrophic velocity and from Ekman transport, based on wind stress, are also included. The climatological monthly heat or freshwater flux at the ocean surface is estimated as the sum of advective and time tendency contributions. The air-sea flux estimates from Argo are described in global maps and basin-wide integrals, in comparison to atmospheric reanalysis data and to air-sea flux products based on observations. This ocean-based estimate of surface fluxes is consistent with property variations in the subsurface ocean and indicates greater amplitude for the climatological monthly heat flux values in the subtropics compared to other products. Similarly, the combination of Argo freshwater flux and reanalysis evaporation, suggests greater amplitude for climatological monthly precipitation in the tropics.

  9. 9 CFR 91.19 - Inspection of ocean vessels prior to loading.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 9 Animals and Animal Products 1 2012-01-01 2012-01-01 false Inspection of ocean vessels prior to... Inspection of ocean vessels prior to loading. It shall be the responsibility of the owners or the masters of an ocean vessel intended for use in exporting livestock to present the vessel to an inspector at...

  10. 9 CFR 91.19 - Inspection of ocean vessels prior to loading.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 9 Animals and Animal Products 1 2013-01-01 2013-01-01 false Inspection of ocean vessels prior to... Inspection of ocean vessels prior to loading. It shall be the responsibility of the owners or the masters of an ocean vessel intended for use in exporting livestock to present the vessel to an inspector at...

  11. 9 CFR 91.19 - Inspection of ocean vessels prior to loading.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 9 Animals and Animal Products 1 2014-01-01 2014-01-01 false Inspection of ocean vessels prior to... Inspection of ocean vessels prior to loading. It shall be the responsibility of the owners or the masters of an ocean vessel intended for use in exporting livestock to present the vessel to an inspector at...

  12. 9 CFR 91.19 - Inspection of ocean vessels prior to loading.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 9 Animals and Animal Products 1 2010-01-01 2010-01-01 false Inspection of ocean vessels prior to... Inspection of ocean vessels prior to loading. It shall be the responsibility of the owners or the masters of an ocean vessel intended for use in exporting livestock to present the vessel to an inspector at...

  13. 9 CFR 91.19 - Inspection of ocean vessels prior to loading.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 9 Animals and Animal Products 1 2011-01-01 2011-01-01 false Inspection of ocean vessels prior to... Inspection of ocean vessels prior to loading. It shall be the responsibility of the owners or the masters of an ocean vessel intended for use in exporting livestock to present the vessel to an inspector at...

  14. Dynamics of ocean surface mixed layer variability in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Schiller, Andreas; Oke, Peter R.

    2015-06-01

    We present a new methodology that allows quantifying the impact of individual terms of the temperature and salinity conservation within the mixed layer on mixed layer depth (MLD). The method is applied to output from an ocean general circulation model in the Indian Ocean to investigate variability and changes in MLD. On seasonal timescales and for most areas of the Indian Ocean variability of MLD is tightly linked to all thermohaline budget terms. In the Indian Ocean at approximately 20°S the MLD covaries with surface heat and freshwater fluxes on intraseasonal and interannual timescales. The geography of the region includes the Leeuwin Current, plus the tropical eastern Indian Ocean for interannual surface freshwater fluxes. The range of seasonal amplitudes of MLD variability varies with individual budget terms but is typically within 1 m/month to 100 m/month. The ocean footprints of an intraseasonal tropical cyclone, tropical and midlatitude seasonal temperature and salinity budgets and interannual variability associated with the Indian Ocean Dipole Mode are analyzed. The results reveal close relationships of the thermohaline budgets within the mixed layer with the variability of the MLD. The associated tendencies of changes in MLD are consistent with Argo and satellite-based observations of tendencies within the mixed layer and sea-surface temperature and salinity.

  15. Consequences of future increased Arctic runoff on Arctic Ocean stratification, circulation, and sea ice cover

    NASA Astrophysics Data System (ADS)

    Nummelin, Aleksi; Ilicak, Mehmet; Li, Camille; Smedsrud, Lars H.

    2016-01-01

    The Arctic Ocean has important freshwater sources including river runoff, low evaporation, and exchange with the Pacific Ocean. In the future, we expect even larger freshwater input as the global hydrological cycle accelerates, increasing high-latitude precipitation, and river runoff. Previous modeling studies show some robust responses to high-latitude freshwater perturbations, including a strengthening of Arctic stratification and a weakening of the large-scale ocean circulation; some idealized modeling studies also document a stronger cyclonic circulation within the Arctic Ocean itself. With the broad range of scales and processes involved, the overall effect of increasing runoff requires an understanding of both the local processes and the broader linkages between the Arctic and surrounding oceans. Here we adopt a more comprehensive modeling approach by increasing river runoff to the Arctic Ocean in a coupled ice-ocean general circulation model, and show contrasting responses in the polar and subpolar regions. Within the Arctic, the stratification strengthens, the halocline and Atlantic Water layer warm, and the cyclonic circulation spins up, in agreement with previous work. In the subpolar North Atlantic, the model simulates a colder and fresher water column with weaker barotropic circulation. In contrast to the estuarine circulation theory, the volume exchange between the Arctic Ocean and the surrounding oceans does not increase with increasing runoff. While these results are robust in our model, we require experiments with other model systems and more complete observational syntheses to better constrain the sensitivity of the climate system to high-latitude freshwater perturbations.

  16. Linking the 8.2 ka Event and its Freshwater Forcing in the Labrador Sea

    NASA Technical Reports Server (NTRS)

    Hoffman, Jeremy S.; Carlson, Anders E.; Winsor, Kelsey; Klinkhammer, Gary P.; LeGrande, Allegra N.; Andrews, John T.; Strasser, C.

    2012-01-01

    The 8.2 ka event was the last deglacial abrupt climate event. A reduction in the Atlantic meridional overturning circulation (AMOC) attributed to the drainage of glacial Lake Agassiz may have caused the event, but the freshwater signature of Lake Agassiz discharge has yet to be identified in (delta)18O of foraminiferal calcite records from the Labrador Sea, calling into question the connection between freshwater discharge to the North Atlantic and AMOC strength. Using Mg/Ca-paleothermometry, we demonstrate that approx. 3 C of near-surface ocean cooling masked an 1.0 % decrease in western Labrador Sea (delta)18O of seawater concurrent with Lake Agassiz drainage. Comparison with North Atlantic (delta)18O of seawater records shows that the freshwater discharge was transported to regions of deep-water formation where it could perturb AMOC and force the 8.2 ka event.

  17. Recent increases in Arctic freshwater flux affects Labrador Sea convection and Atlantic overturning circulation

    PubMed Central

    Yang, Qian; Dixon, Timothy H.; Myers, Paul G.; Bonin, Jennifer; Chambers, Don; van den Broeke, M. R.

    2016-01-01

    The Atlantic Meridional Overturning Circulation (AMOC) is an important component of ocean thermohaline circulation. Melting of Greenland's ice sheet is freshening the North Atlantic; however, whether the augmented freshwater flux is disrupting the AMOC is unclear. Dense Labrador Sea Water (LSW), formed by winter cooling of saline North Atlantic water and subsequent convection, is a key component of the deep southward return flow of the AMOC. Although LSW formation recently decreased, it also reached historically high values in the mid-1990s, making the connection to the freshwater flux unclear. Here we derive a new estimate of the recent freshwater flux from Greenland using updated GRACE satellite data, present new flux estimates for heat and salt from the North Atlantic into the Labrador Sea and explain recent variations in LSW formation. We suggest that changes in LSW can be directly linked to recent freshening, and suggest a possible link to AMOC weakening. PMID:26796579

  18. Recent increases in Arctic freshwater flux affects Labrador Sea convection and Atlantic overturning circulation

    NASA Astrophysics Data System (ADS)

    Yang, Qian; Dixon, Timothy H.; Myers, Paul G.; Bonin, Jennifer; Chambers, Don; van den Broeke, M. R.

    2016-01-01

    The Atlantic Meridional Overturning Circulation (AMOC) is an important component of ocean thermohaline circulation. Melting of Greenland's ice sheet is freshening the North Atlantic; however, whether the augmented freshwater flux is disrupting the AMOC is unclear. Dense Labrador Sea Water (LSW), formed by winter cooling of saline North Atlantic water and subsequent convection, is a key component of the deep southward return flow of the AMOC. Although LSW formation recently decreased, it also reached historically high values in the mid-1990s, making the connection to the freshwater flux unclear. Here we derive a new estimate of the recent freshwater flux from Greenland using updated GRACE satellite data, present new flux estimates for heat and salt from the North Atlantic into the Labrador Sea and explain recent variations in LSW formation. We suggest that changes in LSW can be directly linked to recent freshening, and suggest a possible link to AMOC weakening.

  19. Inland oil spills: Options for minimizing environmental impacts of freshwater spill response

    SciTech Connect

    Not Available

    1994-09-01

    Selecting appropriate protection, response, and cleanup techniques, both before and following an oil spill, affects the ultimate environmental impact and cost resulting from a spill. The American Petroleum Institute (API) and the National Oceanic and Atmospheric Administration (NOAA) jointly developed this guide as a tool for contingency planners and field responders to identify response techniques that have minimal ecological impacts and also minimize the impact of the oil. The guide provides information on 29 response methods and classifies their relative environmental impact for combinations of four oil types and twelve freshwater environments and habitats. Spill topics of special concern in freshwater settings are also discussed, including public health, conditions under which oil might sink in freshwater, oil behavior in ice conditions, permafrost, and use of firefighting foams.

  20. The effects of freshwater flushing on marine heterotrophic protists--implications for ballast water management.

    PubMed

    Hlsmann, N; Galil, B S

    2001-11-01

    Survivorship of ballast-entrained marine heterotrophic protists was examined following freshwater flushing. The recovered taxa, including typical marine rhizopods such as Platyamoeba murchelanoi, Labyrinthula spp, Pontifex maximus, Thecamoeba orbis, and the ciliate Condylostoma arenarium, were reared in waters of various salinities. After 2 months, the original salinity subsample retained five protist taxa, the freshwater six, including the amoeba Cochliopodium bilimbosum, the brackish water 22 taxa, and the seawater 19 taxa. Since protists form a major component of marine microbial food webs, their survival may be instrumental in supporting complex ballast-entrained food webs. Our study raises questions as to the reliability of open-ocean exchange (OOE) or freshwater flushing as effective control measures. PMID:11763219

  1. Recent increases in Arctic freshwater flux affects Labrador Sea convection and Atlantic overturning circulation.

    PubMed

    Yang, Qian; Dixon, Timothy H; Myers, Paul G; Bonin, Jennifer; Chambers, Don; van den Broeke, M R

    2016-01-01

    The Atlantic Meridional Overturning Circulation (AMOC) is an important component of ocean thermohaline circulation. Melting of Greenland's ice sheet is freshening the North Atlantic; however, whether the augmented freshwater flux is disrupting the AMOC is unclear. Dense Labrador Sea Water (LSW), formed by winter cooling of saline North Atlantic water and subsequent convection, is a key component of the deep southward return flow of the AMOC. Although LSW formation recently decreased, it also reached historically high values in the mid-1990s, making the connection to the freshwater flux unclear. Here we derive a new estimate of the recent freshwater flux from Greenland using updated GRACE satellite data, present new flux estimates for heat and salt from the North Atlantic into the Labrador Sea and explain recent variations in LSW formation. We suggest that changes in LSW can be directly linked to recent freshening, and suggest a possible link to AMOC weakening. PMID:26796579

  2. The Impact of Salinity Perturbations on the Future Uptake of Heat By the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Smith, R. S.; Gregory, J. M.; Sutton, R.

    2014-12-01

    Ocean uptake of anthropogenic warming is a key factor in determining the rate of surface climate change and sea-level rise. There is considerable uncertainty in the detail of how the surface freshwater forcing of the ocean will change, which may significantly impact ocean heat uptake. Here, we investigate this by adding either freshwater or salt to the Atlantic in global climate model simulations, simultaneously imposing an idealised atmospheric CO2 scenario. Whilst circulation changes are roughly equal and opposite for salt and freshwater perturbations, freshwater perturbations cause a net increase in Atlantic heat content but salt perturbations produce only small changes in heat content compared to the baseline CO2 scenario. Approximately 15% of the increase in Atlantic heat content in our climate change experiments is due to changes in the Atlantic overturning circulation. The processes active in our model appear robust, although their net result depends on model- and experiment-dependent details.

  3. Rapid seawater circulation through animal burrows in mangrove forests - A significant source of saline groundwater to the tropical coastal ocean

    NASA Astrophysics Data System (ADS)

    Clark, J. F.; Stieglitz, T. C.; Hancock, G. J.

    2010-12-01

    A common approach for quantifying rates of submarine groundwater discharge (SGD) to the coastal ocean is to use geochemical tracers that are part of the U- and Th-decay chains such as Rn-222 and short lived radium isotopes. These radionuclides are naturally enriched in groundwater relative to seawater and have well understood chemistries within the marine environment. They occur in both fresh (continental) and saline (marine) groundwaters and thus the water source is often ambiguous. Stieglitz (2005, Marine Pollution Bulletin 51, 51-59) has shown that some coastal areas within the Great Barrier Reef (GBR) lagoon (Australia) are enriched in the SGD tracer, Rn-222; he attributed this to four possible processes including the tidal flushing of mangrove forest floors. Here, we present a detailed investigation into the tidal circulation of seawater through animal burrows using Rn-222 and isotopes of radium in the Coral Creek mangrove forest, Hinchinbrook Island, Queensland, Australia. The study was conducted at the end of the dry season in a creek with no freshwater inputs. Significant export of radionuclides and salt from the forest into the creek indicates continuous tidally driven circulation through the burrows. Results demonstrate that the forest sediment is efficiently flushed, with a water flux of about 30 L/m2/ day of forest floor, which is equivalent to flushing about 10% of the total burrow volume per tidal cycle. Annual average circulation flux through mangrove forest floors are of the same order as annual river discharge in the central GBR. However, unlike the river discharge, the tidal circulation should be relatively stable throughout the year. This work documents the importance of animal burrows in maintaining productive sediments in these systems, and illustrates the physical process that supports large exports of organic and inorganic matter from mangrove forests to the coastal zone. It also illustrates the importance of considering saline groundwater sources when interpreting SGD radionuclide tracers in the coastal ocean.

  4. 7 CFR 1280.106 - Exporter.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE LAMB PROMOTION, RESEARCH, AND INFORMATION ORDER Lamb Promotion, Research, and Information Order Definitions 1280.106 Exporter. Exporter means any person who exports domestic live lambs from the United States....

  5. 7 CFR 1280.106 - Exporter.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE LAMB PROMOTION, RESEARCH, AND INFORMATION ORDER Lamb Promotion, Research, and Information Order Definitions 1280.106 Exporter. Exporter means any person who exports domestic live lambs from the United States....

  6. 7 CFR 1280.106 - Exporter.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE LAMB PROMOTION, RESEARCH, AND INFORMATION ORDER Lamb Promotion, Research, and Information Order Definitions 1280.106 Exporter. Exporter means any person who exports domestic live lambs from the United States....

  7. 7 CFR 1280.106 - Exporter.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE LAMB PROMOTION, RESEARCH, AND INFORMATION ORDER Lamb Promotion, Research, and Information Order Definitions 1280.106 Exporter. Exporter means any person who exports domestic live lambs from the United States....

  8. 7 CFR 1280.106 - Exporter.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE LAMB PROMOTION, RESEARCH, AND INFORMATION ORDER Lamb Promotion, Research, and Information Order Definitions 1280.106 Exporter. Exporter means any person who exports domestic live lambs from the United States....

  9. 10 CFR 430.65 - Exported products.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... covered product if (a) such covered product is manufactured, sold, or held for sale for export from the United States (or such product was imported for export), unless such product is, in fact, distributed in... product is intended for export....

  10. 7 CFR 1218.6 - Exporter.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE BLUEBERRY PROMOTION, RESEARCH, AND INFORMATION ORDER Blueberry Promotion, Research, and Information Order Definitions § 1218.6 Exporter. Exporter means a person involved in exporting blueberries from another country to the United States....

  11. 7 CFR 1218.6 - Exporter.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE BLUEBERRY PROMOTION, RESEARCH, AND INFORMATION ORDER Blueberry Promotion, Research, and Information Order Definitions § 1218.6 Exporter. Exporter means a person involved in exporting blueberries from another country to the United States....

  12. 7 CFR 1218.6 - Exporter.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE BLUEBERRY PROMOTION, RESEARCH, AND INFORMATION ORDER Blueberry Promotion, Research, and Information Order Definitions § 1218.6 Exporter. Exporter means a person involved in exporting blueberries from another country to the United States....

  13. 7 CFR 1218.6 - Exporter.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE BLUEBERRY PROMOTION, RESEARCH, AND INFORMATION ORDER Blueberry Promotion, Research, and Information Order Definitions § 1218.6 Exporter. Exporter means a person involved in exporting blueberries from another country to the United States....

  14. 7 CFR 1218.6 - Exporter.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE BLUEBERRY PROMOTION, RESEARCH, AND INFORMATION ORDER Blueberry Promotion, Research, and Information Order Definitions § 1218.6 Exporter. Exporter means a person involved in exporting blueberries from another country to the United States....

  15. What is the future fate of estuaries given nutrient over-enrichment, freshwater diversion and low flows?

    PubMed

    Flemer, David A; Champ, Michael A

    2006-03-01

    Freshwater inflow is central to the definition of estuaries and if we lose control of the quantity of freshwater flow or discharge (including seasonal timing) to estuaries, then freshwater water quality has the potential to become a moot issue in estuarine ecosystems (Definition of estuaries: estuaries (aestus = tide) are physico-chemically, geomorphically, and biotically diverse ecosystems. Although numerous definitions of estuaries exist, we prefer the following: an estuary is a partially enclosed coastal water body in which freshwater runoff, often seasonally and episodically pulsed, dilutes salty ocean water and the biotic structure is influenced by dynamic tidal action and associated salinity gradients and reef building organisms and wetlands influence development and evolution of ecological structure and function (see for expanded definition)). PMID:16426644

  16. Metagenomic insights into the evolution, function, and complexity of the planktonic microbial community of Lake Lanier, a temperate freshwater ecosystem.

    PubMed

    Oh, Seungdae; Caro-Quintero, Alejandro; Tsementzi, Despina; DeLeon-Rodriguez, Natasha; Luo, Chengwei; Poretsky, Rachel; Konstantinidis, Konstantinos T

    2011-09-01

    Lake Lanier is an important freshwater lake for the southeast United States, as it represents the main source of drinking water for the Atlanta metropolitan area and is popular for recreational activities. Temperate freshwater lakes such as Lake Lanier are underrepresented among the growing number of environmental metagenomic data sets, and little is known about how functional gene content in freshwater communities relates to that of other ecosystems. To better characterize the gene content and variability of this freshwater planktonic microbial community, we sequenced several samples obtained around a strong summer storm event and during the fall water mixing using a random whole-genome shotgun (WGS) approach. Comparative metagenomics revealed that the gene content was relatively stable over time and more related to that of another freshwater lake and the surface ocean than to soil. However, the phylogenetic diversity of Lake Lanier communities was distinct from that of soil and marine communities. We identified several important genomic adaptations that account for these findings, such as the use of potassium (as opposed to sodium) osmoregulators by freshwater organisms and differences in the community average genome size. We show that the lake community is predominantly composed of sequence-discrete populations and describe a simple method to assess community complexity based on population richness and evenness and to determine the sequencing effort required to cover diversity in a sample. This study provides the first comprehensive analysis of the genetic diversity and metabolic potential of a temperate planktonic freshwater community and advances approaches for comparative metagenomics. PMID:21764968

  17. Metagenomic Insights into the Evolution, Function, and Complexity of the Planktonic Microbial Community of Lake Lanier, a Temperate Freshwater Ecosystem ?

    PubMed Central

    Oh, Seungdae; Caro-Quintero, Alejandro; Tsementzi, Despina; DeLeon-Rodriguez, Natasha; Luo, Chengwei; Poretsky, Rachel; Konstantinidis, Konstantinos T.

    2011-01-01

    Lake Lanier is an important freshwater lake for the southeast United States, as it represents the main source of drinking water for the Atlanta metropolitan area and is popular for recreational activities. Temperate freshwater lakes such as Lake Lanier are underrepresented among the growing number of environmental metagenomic data sets, and little is known about how functional gene content in freshwater communities relates to that of other ecosystems. To better characterize the gene content and variability of this freshwater planktonic microbial community, we sequenced several samples obtained around a strong summer storm event and during the fall water mixing using a random whole-genome shotgun (WGS) approach. Comparative metagenomics revealed that the gene content was relatively stable over time and more related to that of another freshwater lake and the surface ocean than to soil. However, the phylogenetic diversity of Lake Lanier communities was distinct from that of soil and marine communities. We identified several important genomic adaptations that account for these findings, such as the use of potassium (as opposed to sodium) osmoregulators by freshwater organisms and differences in the community average genome size. We show that the lake community is predominantly composed of sequence-discrete populations and describe a simple method to assess community complexity based on population richness and evenness and to determine the sequencing effort required to cover diversity in a sample. This study provides the first comprehensive analysis of the genetic diversity and metabolic potential of a temperate planktonic freshwater community and advances approaches for comparative metagenomics. PMID:21764968

  18. Arctic Outflow West of Greenland: Mass and Freshwater Fluxes at Davis Strait

    NASA Astrophysics Data System (ADS)

    Lee, Craig; Curry, Beth; Petrie, Brian; Azetsu-Scott, Kumiko; Gobat, Jason

    2014-05-01

    Eberhard Fahrbach worked to understand the communication between the Arctic and subpolar oceans and its role in modulating Arctic change. This included long-standing leadership in the Arctic-Subarctic Ocean Flux program and the long-term quantification of fluxes east of Greenland, through Fram Strait, the primary pathway for Atlantic water passing into the Arctic and one of two gateways for freshwater flowing out. Freshwater also exits the Arctic west of Greenland, though the Canadian Arctic Archipelago and, to the south, Davis Strait. The strait provides a convenient choke point for monitoring temporal and spatial variability of Arctic outflow while also characterizing a critical upstream boundary condition for Labrador Sea convection. Fluxes through the Strait represent the net integrated Canadian Archipelago throughflow, over 50% of the Arctic's liquid freshwater discharge, modified by terrestrial inputs and oceanic processes during its southward transit through Baffin Bay. By the time they reach Davis Strait, Arctic waters already embody most of the transformations they undergo prior to exerting their influence on the deepwater formation sites in the Labrador Sea. An ongoing program has characterized Davis Strait volume, freshwater and heat flux since September 2004. Measurements include continuous velocity, temperature and salinity time series collected by a moored array, autumn ship-based hydrographic sections and high-resolution sections occupied by autonomous gliders. Moored instrumentation includes novel new instruments that provide temperature and salinity measurements in the critical region neat the ice-ocean interface and measurements over the shallow Baffin and West Greenland shelves, while gliders have captured the first high-resolution wintertime sections across the Strait. These data show large interannual variability in volume and freshwater transport, with no clear trends observed between 2004-2010. Average volume, liquid freshwater and sea ice transports are -1.6 +- 0.2 Sv, -93 +- 6 mSv and -10 +- 1 mSv, respectively (negative indicates southward transport). However, changes in circulation have occurred, as freshwater outflow from Baffin Bay has decreased and warm, salty North Atlantic inflow has increased since 1987-90. Local atmospheric variability within Baffin Bay and the Labrador Sea influence the observed variability in Davis Strait volume transport either directly or indirectly. Large-scale atmospheric teleconnections, such as the AO and NAO, correlate poorly with Davis Strait volume transport and are likely only an indicator of transport variability when the indices are strong.

  19. Greenland freshwater pathways in the sub-Arctic Seas from model experiments with passive tracers

    NASA Astrophysics Data System (ADS)

    Dukhovskoy, Dmitry S.; Myers, Paul G.; Platov, Gennady; Timmermans, Mary-Louise; Curry, Beth; Proshutinsky, Andrey; Bamber, Jonathan L.; Chassignet, Eric; Hu, Xianmin; Lee, Craig M.; Somavilla, Raquel

    2016-01-01

    Accelerating since the early 1990s, the Greenland Ice Sheet mass loss exerts a significant impact on thermohaline processes in the sub-Arctic seas. Surplus freshwater discharge from Greenland since the 1990s, comparable in volume to the amount of freshwater present during the Great Salinity Anomaly events, could spread and accumulate in the sub-Arctic seas, influencing convective processes there. However, hydrographic observations in the Labrador Sea and the Nordic Seas, where the Greenland freshening signal might be expected to propagate, do not show a persistent freshening in the upper ocean during last two decades. This raises the question of where the surplus Greenland freshwater has propagated. In order to investigate the fate, pathways, and propagation rate of Greenland meltwater in the sub-Arctic seas, several numerical experiments using a passive tracer to track the spreading of Greenland freshwater have been conducted as a part of the Forum for Arctic Ocean Modeling and Observational Synthesis effort. The models show that Greenland freshwater propagates and accumulates in the sub-Arctic seas, although the models disagree on the amount of tracer propagation into the convective regions. Results highlight the differences in simulated physical mechanisms at play in different models and underscore the continued importance of intercomparison studies. It is estimated that surplus Greenland freshwater flux should have caused a salinity decrease by 0.06-0.08 in the sub-Arctic seas in contradiction with the recently observed salinification (by 0.15-0.2) in the region. It is surmised that the increasing salinity of Atlantic Water has obscured the freshening signal.

  20. Variability in efficiency of particulate organic carbon export: A model study

    NASA Astrophysics Data System (ADS)

    Henson, Stephanie A.; Yool, Andrew; Sanders, Richard

    2015-01-01

    The flux of organic carbon from the surface ocean to mesopelagic depths is a key component of the global carbon cycle and is ultimately derived from primary production (PP) by phytoplankton. Only a small fraction of organic carbon produced by PP is exported from the upper ocean, referred to as the export efficiency (herein e-ratio). Limited observations of the e-ratio are available, and there is thus considerable interest in using remotely sensed parameters such as sea surface temperature to extrapolate local estimates to global annual export flux. Currently, there are large discrepancies between export estimates derived in this way; one possible explanation is spatial or temporal sampling bias in the observations. Here we examine global patterns in the spatial and seasonal variability in e-ratio and the subsequent effect on export estimates using a high-resolution global biogeochemical model. The model used here represents export as separate slow- and fast-sinking detrital material whose remineralization is respectively temperature dependent and a function of ballasting minerals. We find that both temperature and the fraction of export carried by slow-sinking particles are factors in determining e-ratio, suggesting that current empirical algorithms for e-ratio that only consider temperature are overly simple. We quantify the temporal lag between PP and export, which is greatest in regions of strong variability in PP where seasonal decoupling can result in large e-ratio variability. Extrapolating global export estimates from instantaneous measurements of e-ratio is strongly affected by seasonal variability and can result in errors in estimated export of up to 60%.

  1. Abbreviation of larval development and extension of brood care as key features of the evolution of freshwater Decapoda.

    PubMed

    Vogt, Gnter

    2013-02-01

    The transition from marine to freshwater habitats is one of the major steps in the evolution of life. In the decapod crustaceans, four groups have colonized fresh water at different geological times since the Triassic, the freshwater shrimps, freshwater crayfish, freshwater crabs and freshwater anomurans. Some families have even colonized terrestrial habitats via the freshwater route or directly via the sea shore. Since none of these taxa has ever reinvaded its environment of origin the Decapoda appear particularly suitable to investigate life-history adaptations to fresh water. Evolutionary comparison of marine, freshwater and terrestrial decapods suggests that the reduction of egg number, abbreviation of larval development, extension of brood care and lecithotrophy of the first posthatching life stages are key adaptations to fresh water. Marine decapods usually have high numbers of small eggs and develop through a prolonged planktonic larval cycle, whereas the production of small numbers of large eggs, direct development and extended brood care until the juvenile stage is the rule in freshwater crayfish, primary freshwater crabs and aeglid anomurans. The amphidromous freshwater shrimp and freshwater crab species and all terrestrial decapods that invaded land via the sea shore have retained ocean-type planktonic development. Abbreviation of larval development and extension of brood care are interpreted as adaptations to the particularly strong variations of hydrodynamic parameters, physico-chemical factors and phytoplankton availability in freshwater habitats. These life-history changes increase fitness of the offspring and are obviously favoured by natural selection, explaining their multiple origins in fresh water. There is no evidence for their early evolution in the marine ancestors of the extant freshwater groups and a preadaptive role for the conquest of fresh water. The costs of the shift from relative r- to K-strategy in freshwater decapods are traded-off against fecundity, future reproduction and growth of females and perhaps against size of species but not against longevity of species. Direct development and extension of brood care is associated with the reduction of dispersal and gene flow among populations, which may explain the high degree of speciation and endemism in directly developing freshwater decapods. Direct development and extended brood care also favour the evolution of social systems, which in freshwater decapods range from simple subsocial organization to eusociality. Hermaphroditism and parthenogenesis, which have evolved in some terrestrial crayfish burrowers and invasive open water crayfish, respectively, may enable populations to adapt to restrictive or new environments by spatio-temporal alteration of their socio-ecological characteristics. Under conditions of rapid habitat loss, environmental pollution and global warming, the reduced dispersal ability of direct developers may turn into a severe disadvantage, posing a higher threat of extinction to freshwater crayfish, primary freshwater crabs, aeglids and landlocked freshwater shrimps as compared to amphidromous freshwater shrimps and secondary freshwater crabs. PMID:22891642

  2. Dynamic Proxies of Ocean Circulation in the North Atlantic During the Younger Dryas

    NASA Astrophysics Data System (ADS)

    Praetorius, S.; McManus, J.

    2007-05-01

    The North Atlantic Deep Water (NADW) is a major component of the Atlantic's meridional overturning circulation, which is strongly linked to climate through the sea-to-air heat transfer by water transported from low to high latitudes. Changes in this circulation system have been implicated in the abrupt climate reversal of the Younger Dryas. Previous studies using nutrient proxies such as ?13C and Cd/Ca show a nutrient enrichment in the North Atlantic during the Younger Dryas, reflecting a reduction in the volume of nutrient-depleted NADW. Although valuable, water mass tracers cannot constrain the rate of overturning; a crucial factor in the overall heat flux of deep water formation. Dynamic proxies such as 231Pa/230Th disequilibria and the grain size of deep sea sediments provide tools to measure changes in the vigor of ocean circulation. 231Pa/230Th ratios act as a proxy for the export rate of subsurface waters from the North Atlantic. Changes in the non-cohesive sortable silt (SS) size fraction (10-63?m) of terrigenous sediments reflect variations in the current strength as a result of the relative entrainment capacity of flow velocity. Here we compare the grain size record from site 984, along the Rekjanes Ridge, with 231Pa/230Th data from core GGC5 on the Bermuda Rise. Site 984 is well situated to monitor both the modern deep water overflows and the intermediate depth waters of the glacial period, whereas core GGC5 offers a more basin-wide measure of circulation export. These records indicate similarly robust overturning circulation during the last glacial maximum and Holocene. In contrast, the deglacial period reveals significant reductions in the circulation. The Younger Dryas exhibits the most dramatic decrease in grain size throughout the 20,000 year record, and the 231Pa/230Th data indicate a reduction in export rate that is rivaled only by the first Heinrich iceberg discharge event. The reduction in current strength during the Younger Dryas is concurrent with an increase in ?18O and polar fauna at both sites, indicating colder surface temperatures. The dynamic circulation proxies demonstrate that decreases in the rate of circulation occurred in association with deglacial melting, supporting the hypothesis that freshwater influx can have a dampening effect on the rate of overturning. This confirms the close connection between ocean circulation and such rapid climate oscillations as the Younger Dryas.

  3. Davis Pond Freshwater Prediversion Biomonitoring Study: Freshwater Fisheries and Eagles

    USGS Publications Warehouse

    Jenkins, Jill A.; Bourgeois, E. Beth; Jeske, Clint W.

    2008-01-01

    In January 2001, the construction of the Davis Pond freshwater diversion structure was completed by the U.S. Army Corps of Engineers. The diversion of freshwater from the Mississippi River is intended to mitigate saltwater intrusion from the Gulf of Mexico and to lessen the concomitant loss of wetland areas. In addition to the freshwater inflow, Barataria Bay basin would receive nutrients, increased flows of sediments, and water-borne and sediment-bound compounds. The purpose of this biomonitoring study was, therefore, to serve as a baseline for prediversion concentrations of selected contaminants in bald eagle (Haliaeetus leucocephalus) nestlings (hereafter referred to as eaglets), representative freshwater fish, and bivalves. Samples were collected from January through June 2001. Two similarly designed postdiversion studies, as described in the biological monitoring program, are planned. Active bald eagle nests targeted for sampling eaglet blood (n = 6) were generally located southwest and south of the diversion structure. The designated sites for aquatic animal sampling were at Lake Salvador, at Lake Cataouatche, at Bayou Couba, and along the Mississippi River. Aquatic animals representative of eagle prey were collected. Fish were from three different trophic levels and have varying feeding strategies and life histories. These included herbivorous striped mullet (Mugil cephalus), omnivorous blue catfish (Ictalurus furcatus), and carnivorous largemouth bass (Micropterus salmoides). Three individuals per species were collected at each of the four sampling sites. Freshwater Atlantic rangia clams (Rangia cuneata) were collected at the downstream marsh sites, and zebra mussels (Dreissena spp.) were collected on the Mississippi River. The U.S. Geological Survey (USGS) Biomonitoring of Environmental Status and Trends (BEST) protocols served as guides for fish sampling and health assessments. Fish are useful for monitoring aquatic ecosystems because they accumulate pesticides and other contaminants. Biomarker data on individual fish, generated at the USGS National Wetlands Research Center (Lafayette, La.), included percent white blood cells in whole blood, spleen weight to body weight ratio, liver weight to body weight ratio, condition factor, splenic macrophage aggregates, and liver microsomal 7-ethoxyresorufin-o-deethylase (EROD) activity. Fish age was estimated by comparing total lengths with values from the same species in the Southeast United States as determined from the literature. Contaminant analyses were coordinated by the U.S. Fish and Wildlife Service (USFWS) Analytical Control Facility (Laurel, Md.), where residues of organochlorine (OC) pesticides, total polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), aliphatic hydrocarbons (AHs), and trace elements were determined. The organic contaminant data were generated at the Mississippi State University Chemical Lab (Mississippi State, Miss.), and the inorganic contaminant data were generated by the Texas A&M University Geochemical and Environmental Research Group (College Station, Tex.). Statistical tests were performed to assess relationships among contaminants, fish age, fish species, and collection sites.

  4. 7 CFR 923.15 - Export.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE SWEET CHERRIES GROWN IN DESIGNATED COUNTIES IN WASHINGTON Order Regulating Handling Definitions § 923.15 Export. Export means to ship...

  5. 7 CFR 923.15 - Export.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... ORDERS; FRUITS, VEGETABLES, NUTS), DEPARTMENT OF AGRICULTURE SWEET CHERRIES GROWN IN DESIGNATED COUNTIES IN WASHINGTON Order Regulating Handling Definitions § 923.15 Export. Export means to ship...

  6. 7 CFR 923.15 - Export.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... ORDERS; FRUITS, VEGETABLES, NUTS), DEPARTMENT OF AGRICULTURE SWEET CHERRIES GROWN IN DESIGNATED COUNTIES IN WASHINGTON Order Regulating Handling Definitions § 923.15 Export. Export means to ship...

  7. 7 CFR 923.15 - Export.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE SWEET CHERRIES GROWN IN DESIGNATED COUNTIES IN WASHINGTON Order Regulating Handling Definitions § 923.15 Export. Export means to ship...

  8. 7 CFR 923.15 - Export.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE SWEET CHERRIES GROWN IN DESIGNATED COUNTIES IN WASHINGTON Order Regulating Handling Definitions § 923.15 Export. Export means to ship...

  9. Ocean Acidification

    NASA Astrophysics Data System (ADS)

    Iglesias-Rodriguez, Maria Debora

    The oceans play a central role in the maintenance of life on Earth. Oceans provide extensive ecosystems for marine animals and plants covering two-thirds of the Earth's surface, are essential sources of food, economic activity, and biodiversity, and are central to the global biogeochemical cycles. The oceans are the largest reservoir of carbon in the Planet, and absorb approximately one-third of the carbon emissions that are released to the Earth's atmosphere as a result of human activities. Since the beginning of industrialization, humans have been responsible for the increase in one greenhouse gas, carbon dioxide (CO2), from approximately 280 parts per million (ppm) at the end of the nineteenth century to the current levels of 390ppm. As well as affecting the surface ocean pH, and the organisms living at the ocean surface, these increases in CO2 are causing global mean surface temperatures to rise.

  10. Exporting calcium from cells.

    PubMed

    Guerini, Danilo; Coletto, Luisa; Carafoli, Ernesto

    2005-01-01

    All eukaryotic cells import Ca2+ through a number of variously gated plasma membrane channels. Once inside cells, Ca2+ transmits information to a large number of (enzyme) targets. Eventually, it must be exported again, to prevent the overloading of the cytosol with Ca2+. Two systems export Ca2+ from cells: a high affinity, low capacity Ca2+-ATPase, and a lower affinity, but much larger capacity, Na+/Ca2+ exchanger. The ATPase (commonly called the Ca2+ pump) is the fine-tuner of cell Ca2+, as it functions well even if the concentration of the ion drops below the microM level. It is a large enzyme, with 10 transmembrane domains and a C-terminal cytosolic tail that contains regulatory sites, including a calmodulin-binding domain. Four distinct gene products plus a large number of splice variants have been described. Some are tissue specific, the isoform 2 being specifically expressed in the sensorial cells of the Corti organ in the inner-ear. Its genetic absence causes deafness in mice. Two different families of the Na+/Ca2+ exchanger exist, one of which, originally described in photoreceptors, transports K+ and Ca2+ in exchange for Na+. The exchanger is particularly active in excitable cells, e.g., heart, where the necessity cyclically arises to rapidly eject large amounts of Ca2+. In addition to heart, the exchanger is particularly important to neurons: the cleavage of the most important neuronal isoform (NCX3) by calpains activated by excitotoxic treatments generates Ca2+ overload and eventually cell death. PMID:16102821

  11. Swimming in the USA: Beachgoer Characteristics and Health Outcomes at U.S. Marine and Freshwater Beaches

    EPA Science Inventory

    Swimming in lakes and oceans is popular, but tittle is known about the demographic characteristics, behaviors, and health risks of beachgoers on a national level. Data from a prospective cohort study of beachgoers at multiple marine and freshwater beaches in the USA were used to ...

  12. Impacts of freshwater on the seasonal variations of surface salinity and circulation in the Caspian Sea

    NASA Astrophysics Data System (ADS)

    Birol Kara, A.; Wallcraft, Alan J.; Joseph Metzger, E.; Gunduz, Murat

    2010-06-01

    A fine resolution (?3.3km) version of the HYbrid Coordinate Ocean Model (HYCOM) is developed for the Caspian Sea. The model consists of a hybrid ?-z coordinate system, with ?-coordinates for the upper layers and z-levels below a user-specified depth and in very shallow water. General features of the Caspian Sea HYCOM are presented including the bottom topography, initialization and atmospheric forcing along with river discharge. The climatologically forced model simulation reveals that there is net heat loss (gain) during winter (summer), and that rivers can have significant influence on the freshwater fluxes, especially on the northwestern shelf. There is a strong seasonal cycle in the net surface heat fluxes. The freshwater fluxes are found to be locally dominated by river discharge. In particular, the Volga River, which has very high discharge rate during the summer months, is found to play an important role in driving the seasonal cycle of freshwater fluxes in the North Caspian Sea. Over the basin, the buoyancy fluxes calculated from net heat and freshwater fluxes indicate that buoyancy is much more sensitive to variations in heating than precipitation-evaporation since thermal buoyancy fluxes are much greater than the haline buoyancy fluxes. A set of model simulations further investigates the impact of evaporation, precipitation and river flow on the upper ocean quantities. It is demonstrated that the discharge rate from the Volga River controls the monthly variations in surface salinity fields in the North Caspian Sea.

  13. Influence of water allocation and freshwater inflow on oyster production: a hydrodynamic-oyster population model for Galveston Bay, Texas, USA.

    PubMed

    Powell, Eric N; Klinck, John M; Hofmann, Eileen E; McManus, Margaret A

    2003-01-01

    A hydrodynamic-oyster population model was developed to assess the effect of changes in freshwater inflow on oyster populations in Galveston Bay, Texas, USA. The population model includes the effects of environmental conditions, predators, and the oyster parasite, Perkinsus marinus, on oyster populations. The hydrodynamic model includes the effects of wind stress, river runoff, tides, and oceanic exchange on the circulation of the bay. Simulations were run for low, mean, and high freshwater inflow conditions under the present (1993) hydrology and predicted hydrologies for 2024 and 2049 that include both changes in total freshwater inflow and diversions of freshwater from one primary drainage basin to another. Freshwater diversion to supply the Houston metropolitan area is predicted to negatively impact oyster production in Galveston Bay. Fecundity and larval survivorship both decline. Mortality from Perkinsus marinus increases, but to a lesser extent. A larger negative impact in 2049 relative to 2024 originates from the larger drop in fecundity under that hydrology. Changes in recruitment and mortality, resulting in lowered oyster abundance, occur because the bay volume available for mixing freshwater input from the San Jacinto and Buffalo Bayou drainage basins that drain metropolitan Houston is small in comparison to the volume of Trinity Bay that presently receives the bulk of the bay's freshwater inflow. A smaller volume for mixing results in salinities that decline more rapidly and to a greater extent under conditions of high freshwater discharge.Thus, the decline in oyster abundance results from a disequilibrium between geography and salinity brought about by freshwater diversion. Although the bay hydrology shifts, available hard substrate does not. The simulations stress the fact that it is not just the well-appreciated reduction in freshwater inflow that can result in decreased oyster production. Changing the location of freshwater inflow can also significantly impact the bay environment, even if the total amount of freshwater inflow does not change. PMID:12447579

  14. Single-cell genomics reveal low recombination frequencies in freshwater bacteria of the SAR11 clade

    PubMed Central

    2013-01-01

    Background The SAR11 group of Alphaproteobacteria is highly abundant in the oceans. It contains a recently diverged freshwater clade, which offers the opportunity to compare adaptations to salt- and freshwaters in a monophyletic bacterial group. However, there are no cultivated members of the freshwater SAR11 group and no genomes have been sequenced yet. Results We isolated ten single SAR11 cells from three freshwater lakes and sequenced and assembled their genomes. A phylogeny based on 57 proteins indicates that the cells are organized into distinct microclusters. We show that the freshwater genomes have evolved primarily by the accumulation of nucleotide substitutions and that they have among the lowest ratio of recombination to mutation estimated for bacteria. In contrast, members of the marine SAR11 clade have one of the highest ratios. Additional metagenome reads from six lakes confirm low recombination frequencies for the genome overall and reveal lake-specific variations in microcluster abundances. We identify hypervariable regions with gene contents broadly similar to those in the hypervariable regions of the marine isolates, containing genes putatively coding for cell surface molecules. Conclusions We conclude that recombination rates differ dramatically in phylogenetic sister groups of the SAR11 clade adapted to freshwater and marine ecosystems. The results suggest that the transition from marine to freshwater systems has purged diversity and resulted in reduced opportunities for recombination with divergent members of the clade. The low recombination frequencies of the LD12 clade resemble the low genetic divergence of host-restricted pathogens that have recently shifted to a new host. PMID:24286338

  15. Freshwater Biological Traits Database (Final Report)

    EPA Science Inventory

    Cover of the <span class=Freshwater Biological Traits Database Final Report"> This final report discusses the development of a database of freshwater biolo...

  16. Freshwater Ecology. LC Science Tracer Bullet.

    ERIC Educational Resources Information Center

    Niskern, Diana, Comp.

    Freshwater ecosystems include lakes, ponds, streams, rivers, and certain types of wetlands. This literature and resources guide is not intended to be a comprehensive bibliography on freshwater ecology; the guide is designed--as the name of the series implies--to put the reader or student "on target." Other literature guides related to freshwater…

  17. NATIVE FRESHWATER FISH AND MUSSEL SPECIES RICHNESS

    EPA Science Inventory

    These data represent predicted current distributions of all native freshwater fish and freshwater mussels in the Middle-Atlantic region. The data are available for both 8-digit HUCs and EMAP hexagons and represent total species counts for each spatial unit.

  18. Freshwater Biological Traits Database (Final Report)

    EPA Science Inventory

    Cover of the <span class=Freshwater Biological Traits Database Final Report"> This final report discusses the development of a database of freshwater biolo...

  19. Effects of Pollution on Freshwater Fish.

    ERIC Educational Resources Information Center

    Brungs, W. A.; And Others

    1978-01-01

    Presents a literature review of the effects of pollution on freshwater fish, covering publications of 1976-77. This review includes: (1) water quality; (2) pesticide pollutants; (3) chemical pollutants; (4) miscellaneous pollutants; and (5) physical factors of pollution on freshwater fish. A list of 338 references is also presented. (HM)

  20. Scientific development of a massively parallel ocean climate model. Final report

    SciTech Connect

    Semtner, A.J.; Chervin, R.M.

    1996-09-01

    Over the last three years, very significant advances have been made in refining the grid resolution of ocean models and in improving the physical and numerical treatments of ocean hydrodynamics. Some of these advances have occurred as a result of the successful transition of ocean models onto massively parallel computers, which has been led by Los Alamos investigators. Major progress has been made in simulating global ocean circulation and in understanding various ocean climatic aspects such as the effect of wind driving on heat and freshwater transports. These steps have demonstrated the capability to conduct realistic decadal to century ocean integrations at high resolution on massively parallel computers.

  1. Carbonate dissolution in mixed waters due to ocean acidification

    NASA Astrophysics Data System (ADS)

    Koski, K.; Wilson, J. L.

    2009-12-01

    Much of the anthropogenically released carbon dioxide has been stored as a dissolved gas in the ocean, causing a 0.1 decrease in ocean surface pH, with models predicting that by 2100 the surface ocean pH will be 0.5 below pre-industrial levels. In mixed ocean water - fresh water environments (e.g. estuaries, coastal aquifers, and edges of ice sheets), the decreased ocean pH couples with the mixed water geochemistry to make water more undersaturated with respect to calcium carbonate than ocean acidification alone. Mixed-water calcite dissolution may be one of the first directly observable effects of ocean acidification, as the ocean water and the fresh water can both be saturated with respect to calcium carbonate while their mixture will be undersaturated. We present a basic quantitative model describing mixed water dissolution in coastal or island freshwater aquifers, using temporally changing ocean pH, sea level, precipitation, and groundwater pumping. The model describes the potential for an increased rate of speleogenesis and porosity/permeability development along the lower edge of a fresh water lens aquifer. The model accounts the indirect effects of rising sea level and a growing coastal population on these processes. Applications are to freshwater carbonate aquifers on islands (e.g. the Bahamas) and in coastal areas (e.g. the unconfined Floridan aquifer of the United States, the Yucatan Peninsula of Mexico).

  2. Freshwater Circulation in the Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Wilson, E. A.; Riser, S.

    2012-12-01

    Based on new estimates, the Bay of Bengal receives a net input of approximately 5000 km3 of freshwater each year. This is primarily supplied by the precipitation and river discharge associated with the southwest monsoon. To balance this input, freshwater must be removed from the bay's surface layer at a mean rate of roughly 0.16 Sverdrup. This relatively large transport of freshwater, which could be of major climatological importance, remains poorly understood. In this study, we attempt to construct a seasonal freshwater budget for the Bay of Bengal using available climatological datasets. In particular, we investigate the relative importance of boundary currents, vertical mixing, and interior eddy fluxes in maintaining a closed freshwater budget. These observational findings are compared to simulated outputs from state-of-the-art models such as HYCOM and SODA.

  3. Arctic mass, freshwater and heat fluxes: methods and modelled seasonal variability.

    PubMed

    Bacon, Sheldon; Aksenov, Yevgeny; Fawcett, Stephen; Madec, Gurvan

    2015-10-13

    Considering the Arctic Ocean (including sea ice) as a defined volume, we develop equations describing the time-varying fluxes of mass, heat and freshwater (FW) into, and storage of those quantities within, that volume. The seasonal cycles of fluxes and storage of mass, heat and FW are quantified and illustrated using output from a numerical model. The meanings of 'reference values' and FW fluxes are discussed, and the potential for error through the use of arbitrary reference values is examined. PMID:26347537

  4. Testing massive Arctic sea ice export as a trigger for abrupt climate change

    NASA Astrophysics Data System (ADS)

    Coletti, Anthony; Condron, Alan; Bradley, Raymond

    2014-05-01

    The discharge of freshwater from glacial lakes to the North Atlantic is repeatedly cited as the main trigger for abrupt centennial to millennial length climate change during the last deglaciation. Broecker et al., (1989) was a proponent of this idea suggesting that abrupt re-routing of pro-glacial lake freshwater to the North Atlantic through the St. Lawrence Valley weakened the strength of the AMOC. Yet, evidence for this is lacking, freshwater estimates in these lakes are relatively small and flood durations are rather short (<5 years), suggesting that floods may not have been the only mechanism driving these climate shifts. Using sophisticated ocean modeling, it has been shown that the release of freshwater originating from the Arctic is more effective at weakening the AMOC compared to freshwater released further south. Here we investigate whether the break-up and mobilization of thick Arctic sea-ice would have supplied enough freshwater to the Nordic Seas to sufficiently cause dampening of the AMOC and hinder NADW formation in the sub-polar North Atlantic. We use numerical climate models to assess 1) the maximum thickness of sea ice that can be formed during glacial periods and the volume of freshwater in the ice, 2) the mechanism which caused the collapse and mobilization of arctic sea-ice into the North Atlantic and 3) the impact of melting sea-ice on global ocean circulation. This hypothesis focuses on the potential impacts of sea-ice as a forcing mechanism for abrupt climate change events on geologic time scales.

  5. Hydrography and biogeochemistry of the coastal ocean

    NASA Astrophysics Data System (ADS)

    Naqvi, S. W. A.; Unnikrishnan, A. S.

    The coastal ocean accounts for only 7% of the total oceanic area, but it plays a very important role in biogeochemical cycles. It not only exchanges energy and matter with the open ocean, but terrestrial inputs of materials such as freshwater, sediments, dissolved/particulate nutrients and organic matter by surface runoff and groundwater flow have to pass through it. The processing of these materials in shallow waters is markedly different from that in the open ocean, and the contribution of the former to biogeochemical fluxes is disproportionately large (15% of oceanic primary production, 80% of organic burial, 50% of calcium carbonate deposition, 90% of sedimentary mineralization, and 75-90% of oceanic sink of suspended material carried by rivers). About 90% of the marine fish catch comes from the shallow seas whose overall economic value is estimated to be >40% of the world's ecosystem services and natural capital. Finally, as much as 40% of the world's population lives within 100 km of the coastlines, making the coastal ocean extremely vulnerable to anthropogenic impingement. This chapter first provides an overview of physical processes that differentiate coastal and openocean regions. It then focuses on selected biogeochemical processes that are of relevance to Surface Ocean-Lower Atmosphere Study, and how they are being affected by human activities.

  6. Seasonal Sources of Carbon Exports in a Headwater Stream

    NASA Astrophysics Data System (ADS)

    Argerich, A.; Johnson, S. L.

    2013-12-01

    Climate change is intimately tied to changes in carbon (C) budgets. Understanding the compartments and processes involved in the global C cycle across a landscape is essential to predict future climate change scenarios. While most C budgets focus on terrestrial contributions, river systems contribute to the C cycle by the export of total organic carbon (TOC) and dissolved inorganic carbon (DIC) to the ocean and by exporting CO2 to the atmosphere. Although headwater streams constitute between 60 and 80 percent of fluvial systems their role in the C cycle has often been neglected due to the methodological constrains derived from their heterogeneous morphology. Here we present an analysis of the temporal variation of C export both downstream and evaded to the atmosphere for a headwater stream draining a forested watershed. We relate it to in-stream metabolic processes (respiration and primary production) and to different carbon pools. Specifically, we estimate downstream exports of C in the form of dissolved organic (DOC), dissolved inorganic (DIC), and particulate organic (POC); we estimate the C content in the fine benthic organic matter (FBOM), dead wood, algae, and macroinvertebrate pools; and finally, the amount of CO2 originated and fixed by stream respiration and primary production. Organic exports, both particulate and dissolved, represented 39.7% of the annual downstream export of C while dissolved inorganic C represented 60.3%. Higher exports were observed during periods of high flow (late fall and winter). Highest seasonality in downstream exports was observed for POC (89.5% coefficient of variation in mean monthly fluxes), followed by DOC and DIC (24.3% and 15.9% respectively). Dissolved CO2 had mostly an autochthonous origin during summer (i.e. from stream ecosystem respiration) and originated from allochthonous sources during the rain-dominated months in Oregon (late fall and winter). The stream was net heterotrophic and the amount of C cycled through respiration and primary production had a similar magnitude to the carbon transported downstream in the form of DOC. Future climate scenarios in the Pacific Northwest predict highest flows during winter and longer periods of low flow during late summer. Our results suggest that if these predictions become true there might be a change in the origin of the CO2 evaded to the atmosphere to a more autochthonous origin and a decrease in the rate between downstream C transport and in-stream C processing. All together, these results increase our understanding of the factors controlling carbon exports downstream and to the atmosphere and to better predict future impacts to climate change.

  7. Sustainable Management of Coastal Environments Through Coupled Terrestrial-Coastal Ocean Models

    NASA Astrophysics Data System (ADS)

    Lohrenz, S. E.; Cai, W.; Tian, H.; He, R.; Xue, Z.; Fennel, K.; Hopkinson, C.; Howden, S. D.

    2012-12-01

    Changing climate and land use practices have the potential to dramatically alter coupled hydrologic-biogeochemical processes and associated movement of water, carbon and nutrients through various terrestrial reservoirs into rivers, estuaries, and coastal ocean waters. Consequences of climate- and land use-related changes will be particularly evident in large river basins and their associated coastal outflow regions. The large spatial extent of such systems necessitates a combination of satellite observations and model-based approaches coupled with targeted ground-based site studies to adequately characterize relationships among climate forcing (e.g., wind, precipitation, temperature, solar radiation, humidity, extreme weather), land use practice/land cover change, and transport of materials through watersheds and, ultimately, to coastal regions. Here, we describe a NASA Interdisciplinary Science project that employs an integrated suite of models in conjunction with remotely sensed as well as targeted in situ observations with the objectives of describing processes controlling fluxes on land and their coupling to riverine, estuarine and ocean ecosystems. The objectives of this effort are to 1) assemble and evaluate long term datasets for the assessment of impacts of climate variability, extreme weather events, and land use practices on transport of water, carbon and nitrogen within terrestrial systems and the delivery of materials to waterways and rivers; 2) using the Mississippi River as a testbed, develop and evaluate an integrated suite of models to describe linkages between terrestrial and riverine systems, transport of carbon and nutrients in the Mississippi river and its tributaries, and associated cycling of carbon and nutrients in coastal ocean waters; and 3) evaluate uncertainty in model products and parameters and identify areas where improved model performance is needed through model refinement and data assimilation. The effort employs the Dynamic Land Ecosystem Model (DLEM) to characterize changes in terrestrial hydrogeologic processes and link this to a coupled physical-biological model characterizing ecosystem dynamics in the northern Gulf of Mexico. Comparisons between observed and modeled exports of freshwater, dissolved inorganic nitrogen and dissolved inorganic carbon show good agreement. These export fluxes are then coupled to a 3-dimensional coupled physical-biogeochemical model adapted for the Gulf of Mexico. Extensive model validations have been performed against satellite observed surface chlorophyll, and in-situ measurements including temperature, salinity, nutrient, alkalinity and dissolved inorganic carbon. Significant seasonal and interannual variations in coastal circulation, nutrient and carbon contents, and plankton concentrations are reasonably well simulated by this model. This research will provide information that will contribute to determining an overall carbon balance in North America. Results would also benefit efforts to describe and predict how land use and land cover changes impact coastal water quality including possible effects of coastal eutrophication and hypoxia.

  8. Southern Ocean Iron Experiment (SOFex)

    SciTech Connect

    Coale, Kenneth H.

    2005-07-28

    The Southern Ocean Iron Experiment (SOFeX) was an experiment decades in the planning. It's implementation was among the most complex ship operations that SIO has been involved in. The SOFeX field expedition was successful in creating and tracking two experimentally enriched areas of the Southern Ocean, one characterized by low silicic acid, one characterized by high silicic acid. Both experimental sites were replete with abundant nitrate. About 100 scientists were involved overall. The major findings of this study were significant in several ways: (1) The productivity of the southern ocean is limited by iron availability. (2) Carbon uptake and flux is therefore controlled by iron availability (3) In spite of low silicic acid, iron promotes non-silicious phytoplankton growth and the uptake of carbon dioxide. (4) The transport of fixed carbon from the surface layers proceeds with a C:N ratio that would indicate differential remineralization of nitrogen at shallow depths. (5) These finding have major implications for modeling of carbon export based on nitrate utilization. (6) The general results of the experiment indicate that, beyond other southern ocean enrichment experiments, iron inputs have a much wider impact of productivity and carbon cycling than previously demonstrated. Scientific presentations: Coale, K., Johnson, K, Buesseler, K., 2002. The SOFeX Group. Eos. Trans. AGU 83(47) OS11A-0199. Coale, K., Johnson, K. Buesseler, K., 2002. SOFeX: Southern Ocean Iron Experiments. Overview and Experimental Design. Eos. Trans. AGU 83 (47) OS22D-01. Buesseler, K.,et al. 2002. Does Iron Fertilization Enhance Carbon Sequestration? Particle flux results from the Southern Ocean Iron Experiment. Eos. Trans. AGU 83 (47), OS22D-09. Johnson, K. et al. 2002. Open Ocean Iron Fertilization Experiments From IronEx-I through SOFeX: What We Know and What We Still Need to Understand. Eos. Trans. AGU 83 (47), OS22D-12. Coale, K. H., 2003. Carbon and Nutrient Cycling During the Southern Ocean Iron Enrichment Experiments. Seattle, WA. Geological Society of America. Coale, K., 2003. Open Ocean Iron Enrichment Experiments: What they have told us, what they have not. American Society for Limnology and Oceanography and The Oceanography Society, Honolulu, February 2004. Coale, K., 2004. Recent Research from the Southern Ocean Iron Experiment (SOFeX), in Taking the Heat: What is the impact of ocean fertilization on climate and ocean ecology? Science of earth and sky. AAAS, February 12-16, Seattle, WA

  9. Tidal exchange between a freshwater tidal marsh and an impacted estuary: the Scheldt estuary, Belgium

    NASA Astrophysics Data System (ADS)

    Van Damme, Stefan; Frank, Dehairs; Micky, Tackx; Olivier, Beauchard; Eric, Struyf; Britta, Gribsholt; Oswald, Van Cleemput; Patrick, Meire

    2009-11-01

    Tidal marsh exchange studies are relatively simple tools to investigate the interaction between tidal marshes and estuaries. They have mostly been confined to only a few elements and to saltwater or brackish systems. This study presents mass-balance results of an integrated one year campaign in a freshwater tidal marsh along the Scheldt estuary (Belgium), covering oxygen, nutrients (N, P and Si), carbon, chlorophyll, suspended matter, chloride and sulfate. The role of seepage from the marsh was also investigated. A ranking between the parameters revealed that oxygenation was the strongest effect of the marsh on the estuarine water. Particulate parameters showed overall import. Export of dissolved silica (DSi) was more important than exchange of any other nutrient form. Export of DSi and import of total dissolved nitrogen (DIN) nevertheless contributed about equally to the increase of the Si:N ratio in the seepage water. The marsh had a counteracting effect on the long term trend of nutrient ratios in the estuary.

  10. Ocean dumping

    SciTech Connect

    Not Available

    1982-01-01

    The regulation of the dumping of materials into the ocean is reviewed. Criteria to be applied in reviewing and evaluating permit applications for the transportation and dumping of materials into the ocean are established. A definition of monitoring of dumping sites, the assessment of fees to cover permit processing costs, and a moratorium is placed on the issuance of permits for the disposal of radioactive waste are included.

  11. 77 FR 40493 - Export Administration Regulations

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-07-10

    ... Bureau of Industry and Security 15 CFR Parts 740, 742, 748, 750, 752, and 760 Export Administration... heading of paragraph (d) to read ``Shippers Export Declaration or Automated Export System Record''. 0 2...): Once a mass market classification request is accepted in SNAP-R, you may export and reexport...

  12. 15 CFR 2012.3 - Export certificates.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 15 Commerce and Foreign Trade 3 2011-01-01 2011-01-01 false Export certificates. 2012.3 Section... STATES TRADE REPRESENTATIVE IMPLEMENTATION OF TARIFF-RATE QUOTAS FOR BEEF 2012.3 Export certificates... export certificate is in effect with respect to the beef. (b) To be valid, an export certificate...

  13. 27 CFR 28.154 - Export marks.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2011-04-01 2011-04-01 false Export marks. 28.154..., for Exportation or Transfer to a Foreign-Trade Zone 28.154 Export marks. In addition to the marks... provisions of part 19 of this chapter, the proprietor shall mark the word Export on the Government side...

  14. 27 CFR 28.193 - Export marks.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2011-04-01 2011-04-01 false Export marks. 28.193... Drawback Filing of Notice and Removal 28.193 Export marks. In addition to the marks and brands required... chapter, the exporter shall mark the word Export on the Government side of each case or Government...

  15. 27 CFR 28.223 - Export marks.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2011-04-01 2011-04-01 false Export marks. 28.223... Export marks. In addition to the marks and brands required to be placed on kegs, barrels, cases, crates... Export on each container or case before removal for export, for use on vessels or aircraft, or...

  16. 40 CFR 91.1009 - Export exemptions.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Export exemptions. 91.1009 Section 91....1009 Export exemptions. (a) A new marine SI engine intended solely for export, and so labeled or tagged... regulations. (d) It is a condition of any exemption for the purpose of export under § 91.1004(b) that...

  17. 40 CFR 92.909 - Export exemptions.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Export exemptions. 92.909 Section 92....909 Export exemptions. (a) A new locomotive or locomotive engine intended solely for export, and so... from EPA standards. (c) It is a condition of any exemption for the purpose of export under paragraph...

  18. 40 CFR 94.909 - Export exemptions.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Export exemptions. 94.909 Section 94... Export exemptions. (a) A new engine intended solely for export, and so labeled or tagged on the outside... of export under paragraph (a) of this section, that such exemption is void ab initio with respect...

  19. 40 CFR 89.909 - Export exemptions.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 20 2010-07-01 2010-07-01 false Export exemptions. 89.909 Section 89....909 Export exemptions. (a) A new nonroad engine intended solely for export, and so labeled or tagged... export under paragraph (a) of this section, that such exemption is void ab initio with respect to a...

  20. 27 CFR 28.154 - Export marks.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Export marks. 28.154..., for Exportation or Transfer to a Foreign-Trade Zone 28.154 Export marks. In addition to the marks... provisions of part 19 of this chapter, the proprietor shall mark the word Export on the Government side...

  1. 15 CFR 2012.3 - Export certificates.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 15 Commerce and Foreign Trade 3 2010-01-01 2010-01-01 false Export certificates. 2012.3 Section... STATES TRADE REPRESENTATIVE IMPLEMENTATION OF TARIFF-RATE QUOTAS FOR BEEF 2012.3 Export certificates... export certificate is in effect with respect to the beef. (b) To be valid, an export certificate...

  2. 27 CFR 28.193 - Export marks.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Export marks. 28.193... Drawback Filing of Notice and Removal 28.193 Export marks. In addition to the marks and brands required... chapter, the exporter shall mark the word Export on the Government side of each case or Government...

  3. 27 CFR 28.223 - Export marks.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 27 Alcohol, Tobacco Products and Firearms 1 2010-04-01 2010-04-01 false Export marks. 28.223... Export marks. In addition to the marks and brands required to be placed on kegs, barrels, cases, crates... Export on each container or case before removal for export, for use on vessels or aircraft, or...

  4. 19 CFR 18.42 - Direct exportation.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... the Census (15 CFR part 30) and the Office of Export Control (15 CFR part 386). The port director... 19 Customs Duties 1 2010-04-01 2010-04-01 false Direct exportation. 18.42 Section 18.42 Customs... Under Cover of A Tir Carnet 18.42 Direct exportation. At the port of exportation, the container...

  5. 10 CFR 431.405 - Exported equipment.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... for export from the United States (or such equipment was imported for export), unless such equipment... 10 Energy 3 2010-01-01 2010-01-01 false Exported equipment. 431.405 Section 431.405 Energy... EQUIPMENT General Provisions § 431.405 Exported equipment. Under Sections 330 and 345 of the Act, this...

  6. 10 CFR 431.405 - Exported equipment.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... for export from the United States (or such equipment was imported for export), unless such equipment... 10 Energy 3 2011-01-01 2011-01-01 false Exported equipment. 431.405 Section 431.405 Energy... EQUIPMENT General Provisions § 431.405 Exported equipment. Under Sections 330 and 345 of the Act, this...

  7. Multidrug-exporting secondary transporters.

    PubMed

    Murakami, Satoshi; Yamaguchi, Akihito

    2003-08-01

    The major cause of intrinsic drug resistance in Gram-negative bacteria is a resistance nodulation division type multidrug exporter, which couples with an outer membrane channel and a membrane fusion protein and exports drugs out of the cell, bypassing the periplasm; this process is driven by proton motive force. A recent crystal structure determination of a major resistance nodulation division type multidrug exporter, AcrB in Escherichia coli, greatly advances our understanding of the multidrug export mechanism. The most striking feature of the AcrB trimer is the presence of three vestibules open to the periplasm at the boundary between the periplasmic headpiece and the transmembrane region. Substrates can gain access to the central cavity from the periplasmic surface of the cytoplasmic membrane and are then actively transported through the extramembrane pore into the outer membrane channel TolC, via the funnel at the top of the AcrB headpiece. PMID:12948774

  8. Net removal of major marine dissolved organic carbon fractions in the subsurface ocean

    NASA Astrophysics Data System (ADS)

    Hansell, Dennis A.; Carlson, Craig A.; Schlitzer, Reiner

    2012-03-01

    Marine dissolved organic matter is a massive reservoir of carbon holding >200x the ocean biomass inventory. Primarily produced at the ocean surface and then exported to depth with overturn of the water column, this carbon can be sequestered in the ocean interior for centuries. Understanding the loss of dissolved organic carbon (DOC) upon export has been data limited, but recent global ocean surveys are overcoming that problem. Here we characterize three fractions of exported carbon by apparent continuity in removal rates: semi-labile and semi-refractory, summing to 20 PgC, and the balance as refractory DOC. Distinct lifetimes coupled with ocean circulation control where the fractions are exported to depth, and thus the carbon sequestration time scales. Maximum remineralization rates of exported DOC occur in the convergent subtropical gyres, where a range of 500 to <1500 mmol C m-2 yr-1 can exceed remineralization of sinking biogenic particles. Regions of high particle export production and highly stratified systems exhibit minimal exported DOC remineralization.

  9. Catchment controls on solute export

    NASA Astrophysics Data System (ADS)

    Musolff, Andreas; Schmidt, Christian; Selle, Benny; Fleckenstein, Jan H.

    2015-12-01

    Dynamics of solute export from catchments can be classified in terms of chemostatic and chemodynamic export regimes by an analysis of concentration-discharge relationships. Previous studies hypothesized that distinct export regimes emerge from the presence of solute mass stores within the catchment and their connectivity to the stream. However, so far a direct link of solute export to identifiable catchment characteristics is missing. Here we investigate long-term time series of stream water quality and quantity of nine neighboring catchments in Central Germany ranging from relatively pristine mountain catchments to agriculturally dominated lowland catchments, spanning large gradients in land use, geology, and climatic conditions. Given the strong collinearity of catchment characteristics we used partial least square regression analysis to quantify the predictive power of these characteristics for median concentrations and the metrics of export regime. We can show that median concentrations and metrics of the export regimes of major ions and nutrients can indeed be inferred from catchment characteristics. Strongest predictors for median concentrations were the share of arable land, discharge per area, runoff coefficient and available water capacity in the root zone of the catchments. The available water capacity in the root zone, the share of arable land being artificially drained and the topographic gradient were found to be the most relevant predictors for the metrics of export regime. These catchment characteristics can represent the size of solute mass store such as the fraction of arable land being a measure for the store of nitrate. On the other hand, catchment characteristics can be a measure for the connectivity of these solute stores to the stream such as the fraction of tile drained land in the catchments. This study demonstrates the potential of data-driven, top down analyses using simple metrics to classify and better understand dominant controls of solute export from catchments.

  10. Pathogenic agents in freshwater resources

    NASA Astrophysics Data System (ADS)

    Geldreich, Edwin E.

    1996-02-01

    Numerous pathogenic agents have been found in freshwaters used as sources for water supplies, recreational bathing and irrigation. These agents include bacterial pathogens, enteric viruses, several protozoans and parasitic worms more common to tropical waters. Although infected humans are a major source of pathogens, farm animals (cattle, sheep, pigs), animal pets (dogs, cats) and wildlife serve as significant reservoirs and should not be ignored. The range of infected individuals within a given warm-blooded animal group (humans included) may range from 1 to 25%. Survival times for pathogens in the water environment may range from a few days to as much as a year (Ascaris, Taenia eggs), with infective dose levels varying from one viable cell for several primary pathogenic agents to many thousands of cells for a given opportunistic pathogen.As pathogen detection in water is complex and not readily incorporated into routine monitoring, a surrogate is necessary. In general, indicators of faecal contamination provide a positive correlation with intestinal pathogen occurrences only when appropriate sample volumes are examined by sensitive methodology.Pathways by which pathogens reach susceptible water users include ingestion of contaminated water, body contact with polluted recreational waters and consumption of salad crops irrigated by polluted freshwaters. Major contributors to the spread of various water-borne pathogens are sewage, polluted surface waters and stormwater runoff. All of these contributions are intensified during periods of major floods. Several water-borne case histories are cited as examples of breakdowns in public health protection related to water supply, recreational waters and the consumption of contaminated salad crops. In the long term, water resource management must focus on pollution prevention from point sources of waste discharges and the spread of pathogens in watershed stormwater runoff.

  11. Arctic Freshwater Synthesis: Summary of key emerging issues

    NASA Astrophysics Data System (ADS)

    Prowse, T.; Bring, A.; Mrd, J.; Carmack, E.; Holland, M.; Instanes, A.; Vihma, T.; Wrona, F. J.

    2015-10-01

    In response to a joint request from the World Climate Research Program's Climate and Cryosphere Project, the International Arctic Science Committee, and the Arctic Council's Arctic Monitoring and Assessment Program an updated scientific assessment has been conducted of the Arctic Freshwater System (AFS), entitled the Arctic Freshwater Synthesis (AFS?). The major reason behind the joint request was an increasing concern that changes to the AFS have produced, and could produce even greater, changes to biogeophysical and socioeconomic systems of special importance to northern residents and also produce extra-Arctic climatic effects that will have global consequences. The AFS? was structured around six key thematic areas: atmosphere, oceans, terrestrial hydrology, terrestrial ecology, resources, and modeling, the review of each coauthored by an international group of scientists and published as separate manuscripts in this special issue of Journal of Geophysical Research-Biogeosciences. This AFS? summary manuscript reviews key issues that emerged during the conduct of the synthesis, especially those that are cross-thematic in nature, and identifies future research required to address such issues.

  12. Biodiversity and distribution of polar freshwater DNA viruses.

    PubMed

    Aguirre de Cárcer, Daniel; López-Bueno, Alberto; Pearce, David A; Alcamí, Antonio

    2015-06-01

    Viruses constitute the most abundant biological entities and a large reservoir of genetic diversity on Earth. Despite the recent surge in their study, our knowledge on their actual biodiversity and distribution remains sparse. We report the first metagenomic analysis of Arctic freshwater viral DNA communities and a comparative analysis with other freshwater environments. Arctic viromes are dominated by unknown and single-stranded DNA viruses with no close relatives in the database. These unique viral DNA communities mostly relate to each other and present some minor genetic overlap with other environments studied, including an Arctic Ocean virome. Despite common environmental conditions in polar ecosystems, the Arctic and Antarctic DNA viromes differ at the fine-grain genetic level while sharing a similar taxonomic composition. The study uncovers some viral lineages with a bipolar distribution, suggesting a global dispersal capacity for viruses, and seemingly indicates that viruses do not follow the latitudinal diversity gradient known for macroorganisms. Our study sheds light into the global biogeography and connectivity of viral communities. PMID:26601189

  13. Biodiversity and distribution of polar freshwater DNA viruses

    PubMed Central

    Aguirre de Cárcer, Daniel; López-Bueno, Alberto; Pearce, David A.; Alcamí, Antonio

    2015-01-01

    Viruses constitute the most abundant biological entities and a large reservoir of genetic diversity on Earth. Despite the recent surge in their study, our knowledge on their actual biodiversity and distribution remains sparse. We report the first metagenomic analysis of Arctic freshwater viral DNA communities and a comparative analysis with other freshwater environments. Arctic viromes are dominated by unknown and single-stranded DNA viruses with no close relatives in the database. These unique viral DNA communities mostly relate to each other and present some minor genetic overlap with other environments studied, including an Arctic Ocean virome. Despite common environmental conditions in polar ecosystems, the Arctic and Antarctic DNA viromes differ at the fine-grain genetic level while sharing a similar taxonomic composition. The study uncovers some viral lineages with a bipolar distribution, suggesting a global dispersal capacity for viruses, and seemingly indicates that viruses do not follow the latitudinal diversity gradient known for macroorganisms. Our study sheds light into the global biogeography and connectivity of viral communities. PMID:26601189

  14. Rapid and early export of Phaeocystis antarctica blooms in the Ross Sea, Antarctica.

    PubMed

    DiTullio, G R; Grebmeier, J M; Arrigo, K R; Lizotte, M P; Robinson, D H; Leventer, A; Barry, J P; VanWoert, M L; Dunbar, R B

    2000-04-01

    The Southern Ocean is very important for the potential sequestration of carbon dioxide in the oceans and is expected to be vulnerable to changes in carbon export forced by anthropogenic climate warming. Annual phytoplankton blooms in seasonal ice zones are highly productive and are thought to contribute significantly to pCO2 drawdown in the Southern Ocean. Diatoms are assumed to be the most important phytoplankton class with respect to export production in the Southern Ocean; however, the colonial prymnesiophyte Phaeocystis antarctica regularly forms huge blooms in seasonal ice zones and coastal Antarctic waters. There is little evidence regarding the fate of carbon produced by P. antarctica in the Southern Ocean, although remineralization in the upper water column has been proposed to be the main pathway in polar waters. Here we present evidence for early and rapid carbon export from P. antarctica blooms to deep water and sediments in the Ross Sea. Carbon sequestration from P. antarctica blooms may influence the carbon cycle in the Southern Ocean, especially if projected climatic changes lead to an alteration in the structure of the phytoplankton community. PMID:10766240

  15. The Oceanic Biogeochemical Cycle of Zinc and Its Isotopes

    NASA Astrophysics Data System (ADS)

    Vance, D.; Little, S. H.; de Souza, G. F.; Cullen, J. T.; Lohan, M. C.

    2014-12-01

    Zinc (Zn) is the most abundant trace metal in the phytoplankton that dominate vertical carbon export in the ocean, the diatoms. But the strong relationship between the vertical distributions of Zn and the silicon (Si) that makes up the opal hard parts of diatoms represents a long-standing puzzle. Zn is overwhelmingly co-located with phosphate in the organic matter of diatom cells, not with Si in opal, and is regenerated with phosphate in the upper ocean, not with Si in the deep. The resolution of this apparent paradox is key both to an understanding of the global oceanic cycling of Zn, and to the rates and mechanisms by which biologically-assimilated trace metals are returned to the photic zone. Here, we show that oceanic dissolved Zn exhibits significant isotopic variation in the upper ocean that is consistent with vertical cycling. However, we suggest that the isotopically homogeneous global deep ocean Zn pool is largely sourced from the Southern Ocean. This leads to a new view of the global oceanic cycling of this important trace metal, one that is consistent with the unique physiology of Southern Ocean diatoms, the coupling of Zn and Si in the global deep ocean, and the emerging paradigm for global ocean nutrient dynamics. Our data and interpretation imply a small Zn pool that is biologically cycled in the upper ocean, but is to a great extent decoupled from the much larger Southern-Ocean-dominated deep ocean pool.

  16. Hotspots in ground and surface water carbon fluxes through a freshwater to marine (mangrove) transition zone

    NASA Astrophysics Data System (ADS)

    Larsen, J.; Welti, N.; Hayes, M.; Lockington, D. A.

    2014-12-01

    The transfer of carbon and water from coastal freshwater wetlands to intertidal and marine zones is significant for sustaining ecosystem processes, particularly within mangroves environments. Large increases in carbon and nutrient fluxes within spatially confined zones (hotspots) are significant as drivers for broader cycling. How these processes relate to the transfers between surface and groundwater systems, as well as the transition from freshwater to marine environments, remains poorly understood. We investigated the flux of carbon and water from a freshwater wetland, to a saltmarsh and then mangroves, both within the main surface channel and within a comprehensive shallow groundwater bore network. We were able to characterise the main spatial trends in water gradients and mixing (using salinity, hydraulic gradients, stable water isotopes, and temperature) over seasonal cycles. In addition, at the same time we investigated the changes in dissolved organic carbon concentration and quality (fluorescence, UV), as well as nutrients (NO3, NH4). This revealed the river and tidal channel to be a significant export pathway for organic carbon, which was generally highly aromatic and recalcitrant. However, we also found that isolated sections of the brackish groundwater mixing zone between freshwater and marine provided a consistently high DOC 'hotspot' of very high quality carbon. This hotspot has high lateral groundwater gradients and therefore likely transports this carbon to the rest of the mangrove subsurface, where it is rapidly assimilated. These results imply large spatial heterogeneity in the carbon cycling between freshwater and marine environments, and have significant implications for the processing of the organic matter, and therefore also the respiration of greenhouse gases such as CO2 and CH4.

  17. Comments on Two stable equilibria of a coupled ocean-atmosphere model'

    SciTech Connect

    Birchfield, G.E. )

    1993-01-01

    Manabe and Stouffer (1988) previously have presented the results of experiments with a global coupled ocean-atmosphere climate model, which suggests that the climate of the earth may be bimodal in character. They couple a general circulation model of the world oceans (OGCM) to a general circulation models of the atmosphere (AGCM) by imposing continuity of heat and freshwater fluxes and stresses at the ocean-atmosphere interface. They attribute the large difference between the results and the modern ocean to a systematic bias in the model surface ocean freshwater flux. The authors of this comment attribute the bias in the MS OAGCM and the necessity of the freshwater flux correction to a failure of the model to adequately simulate surface freshwater fluxes, in particular for the GIN sea. The authors feel that if the GIN Sea is indeed critical, a possible solution may be to use a nested ocean-atmosphere grid in this region similar to that implemented for ocean eddies by Spall and Holland (1991).

  18. 40 CFR 35.1605-3 - Publicly owned freshwater lake.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 40 Protection of Environment 1 2011-07-01 2011-07-01 false Publicly owned freshwater lake. 35.1605... Owned Freshwater Lakes § 35.1605-3 Publicly owned freshwater lake. A freshwater lake that offers public access to the lake through publicly owned contiguous land so that any person has the same opportunity...

  19. 40 CFR 35.1605-3 - Publicly owned freshwater lake.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 40 Protection of Environment 1 2010-07-01 2010-07-01 false Publicly owned freshwater lake. 35.1605... Owned Freshwater Lakes § 35.1605-3 Publicly owned freshwater lake. A freshwater lake that offers public access to the lake through publicly owned contiguous land so that any person has the same opportunity...

  20. Lessons in divergence and convergence in marine and freshwater iron-oxidizing bacteria

    NASA Astrophysics Data System (ADS)

    Emerson, D.; McBeth, J. M.; Fleming, E. J.; Moyer, C. L.

    2011-12-01

    Lithoautotrophic oxygen-dependent Fe-oxidizing bacteria (FeOB) that grow at circumneutral pH are found in marine and freshwater habitats and play an important role in Fe-transformations. These obligately microaerophilic bacteria form unique biogenic Fe minerals that can become fossilized. Their obligate metabolism suggests they may been present during the late Archaean or early Proterozoic when oxygen was in low abundance and high Fe(II) concentrations existed in the ocean. Phylogenetic analysis indicates that members of the marine FeOB community belong to the Zetaproteobacteria, a novel class of Proteobacteria, whereas dominant freshwater FeOB belong to the class Betaproteobacteria. Despite different evolutionary histories, freshwater and marine strains share remarkable morphological and physiological similarities. As an illustration, this work describes the discovery of a sheathed FeOB that grows as a surface film on thick microbial mats composed of FeOB at hydrothermal vents associated with Loihi Seamount, an active undersea volcano. This uncultivated organism bears striking resemblance to the freshwater sheath forming Fe-oxidizer, Leptothrix ochracea; however by using different culture-independent techniques, including specific fluorescence in-situ hybridization (FISH) probes to the SSU rRNA gene, we show that it is not L. ochracea, but a member of the Zetaproteobacteria. The strong morphological similarities between these organisms likely represent a case of convergent evolution. To further constrain relationships between members of the marine and freshwater groups of FeOB we surveyed four iron mat communities along a salinity gradient, from freshwater to near full strength seawater, in a tidal region of the Sheepscot river in Maine. The mat communities were examined microscopically, and all had abundant evidence for biogenically formed iron oxides. Community DNA was extracted from each site and community composition, as assessed by tagged pyrosequencing of V4 region of the SSU rRNA gene, revealed that FeOB related to Betaproteobacteria were most abundant at the freshwater site, but even at low salinity (1-3 ppt), Zetaproteobacteria were present and were dominant at intermediate salinity (10 ppt), where members of the FeOB Betaproteobacteria were not observed. These results were corroborated using appropriate FISH probes. This analysis demonstrated that marine FeOB are capable of growth under a range of salt conditions, while freshwater FeOB are restricted only to freshwater habitats. This has implications for interpretation of biogenic microfossils found in ancient environments.

  1. Global deep ocean oxygenation by enhanced ventilation in the Southern Ocean under long-term global warming

    NASA Astrophysics Data System (ADS)

    Yamamoto, A.; Abe-Ouchi, A.; Shigemitsu, M.; Oka, A.; Takahashi, K.; Ohgaito, R.; Yamanaka, Y.

    2015-10-01

    Global warming is expected to decrease ocean oxygen concentrations by less solubility of surface ocean and change in ocean circulation. The associated expansion of the oxygen minimum zone would have adverse impacts on marine organisms and ocean biogeochemical cycles. Oxygen reduction is expected to persist for a thousand years or more, even after atmospheric carbon dioxide stops rising. However, long-term changes in ocean oxygen and circulation are still unclear. Here we simulate multimillennium changes in ocean circulation and oxygen under doubling and quadrupling of atmospheric carbon dioxide, using a fully coupled atmosphere-ocean general circulation model and an offline biogeochemical model. In the first 500 years, global oxygen concentration decreases, consistent with previous studies. Thereafter, however, the oxygen concentration in the deep ocean globally recovers and overshoots at the end of the simulations, despite surface oxygen decrease and weaker Atlantic meridional overturning circulation. This is because, after the initial cessation, the recovery and overshooting of deep ocean convection in the Weddell Sea enhance ventilation and supply oxygen-rich surface waters to deep ocean. Another contributor to deep ocean oxygenation is seawater warming, which reduces the export production and shifts the organic matter remineralization to the upper water column. Our results indicate that the change in ocean circulation in the Southern Ocean potentially drives millennial-scale oxygenation in deep ocean, which is opposite to the centennial-scale global oxygen reduction and general expectation.

  2. Impact of Freshwater Fluxes on Labrador Sea Dynamics in the Regional Arctic System Model

    NASA Astrophysics Data System (ADS)

    Hossainzadeh, S.; Maslowski, W.; Osinski, R.; Tulaczyk, S. M.

    2014-12-01

    Continental runoff provides a critical freshwater flux into the ocean because it adds time-space varying buoyancy to the coastal ocean. This forcing is linked to the large-scale ocean dynamics and climate via the shelf-basin exchange and its resulting impact on the stratification and ventilation of the interior basin. Here we evaluate the role that a realistic runoff forcing has on the hydrography and dynamics of the Labrador Sea by comparing results from two simulations using a subset of the Regional Arctic System Model (RASM). RASM is a regional earth system model, however in this study the atmospheric (Weather and Research Forecasting - WRF) and land (Variable Infiltration Capacity - VIC) model components are replaced with prescribed realistic atmospheric reanalysis data. Its ocean and sea ice models (Parallel Ocean Program - POP and Los Alamos Sea Ice - CICE models, respectively) are the only model components that are actively coupled via the flux coupler (CPL7). This model has a high spatial resolution of 1/12oin the horizontal and 45 levels in the vertical direction. The results of two simulations are analyzed which vary only in the way that sea surface salinity is determined: i) restored to monthly sea surface salinity climatology, or ii) calculated based on the prescribed surface freshwater fluxes. In the first run, the sea surface salinity is restored to mean monthly climatology from the Polar Science Center Hydrographic Climatology (PHC). In the second run, the surface salinity restoring is turned off and instead more realistic surface liquid freshwater fluxes from land runoff and precipitation minus evaporation (P-E) fluxes are prescribed from the Coordinated Ice-ocean Reference Experiments version 2 (CORE2). We find that the change in surface freshwater forcing creates a substantial difference in: (i) the modeled magnitude and spatial distribution of total kinetic energy, not only at the surface but also at depth, (ii) the sea ice extent and (iii) the spatial distribution and annual cycle of the mixed layer depth in the Labrador Sea. In addition, the hydrographic structure is more realistic in the second run when compared to observations. We further analyze the results in terms of the role that mesoscale eddies play in preconditioning or inhibiting open ocean convection and deep-water formation in the Labrador Sea.

  3. Decadal fingerprints of freshwater discharge around Greenland in a multi-model ensemble

    NASA Astrophysics Data System (ADS)

    Swingedouw, Didier; Rodehacke, Christian B.; Behrens, Erik; Menary, Matthew; Olsen, Steffen M.; Gao, Yongqi; Mikolajewicz, Uwe; Mignot, Juliette; Biastoch, Arne

    2013-08-01

    The recent increase in the rate of the Greenland ice sheet melting has raised with urgency the question of the impact of such a melting on the climate. As former model projections, based on a coarse representation of the melting, show very different sensitivity to this melting, it seems necessary to consider a multi-model ensemble to tackle this question. Here we use five coupled climate models and one ocean-only model to evaluate the impact of 0.1 Sv (1 Sv = 106 m3/s) of freshwater equally distributed around the coast of Greenland during the historical era 1965-2004. The ocean-only model helps to discriminate between oceanic and coupled responses. In this idealized framework, we find similar fingerprints in the fourth decade of hosing among the models, with a general weakening of the Atlantic Meridional Overturning Circulation (AMOC). Initially, the additional freshwater spreads along the main currents of the subpolar gyre. Part of the anomaly crosses the Atlantic eastward and enters into the Canary Current constituting a freshwater leakage tapping the subpolar gyre system. As a consequence, we show that the AMOC weakening is smaller if the leakage is larger. We argue that the magnitude of the freshwater leakage is related to the asymmetry between the subpolar-subtropical gyres in the control simulations, which may ultimately be a primary cause for the diversity of AMOC responses to the hosing in the multi-model ensemble. Another important fingerprint concerns a warming in the Nordic Seas in response to the re-emergence of Atlantic subsurface waters capped by the freshwater in the subpolar gyre. This subsurface heat anomaly reaches the Arctic where it emerges and induces a positive upper ocean salinity anomaly by introducing more Atlantic waters. We found similar climatic impacts in all the coupled ocean-atmosphere models with an atmospheric cooling of the North Atlantic except in the region around the Nordic Seas and a slight warming south of the equator in the Atlantic. This meridional gradient of temperature is associated with a southward shift of the tropical rains. The free surface models also show similar sea-level fingerprints notably with a comma-shape of high sea-level rise following the Canary Current.

  4. The Ocean is Shaping Tropospheric Adjustments

    NASA Astrophysics Data System (ADS)

    Rugenstein, M.; Sedlacek, J.; Knutti, R.

    2014-12-01

    We analyze the ocean's role in shaping the atmosphere's fast response to radiative forcings with a 120-member ensemble of the coupled climate model CESM. Recently, it has been argued that the initial tropospheric adjustment to a forcing agent should be treated as part of the forcing and not as a feedback, as long as the surface temperature response is negligible. In most of these studies, the ocean is not considered to play an active role in the adjustment phase. We show that on time scales of months to years after a forcing, the ocean heat uptake (OHU) strongly varies spatially. While the tropical Pacific initially loses heat, locations of high OHU shift poleward during the first three years, before becoming stationary. The ocean is passively and actively linked to the atmospheric fast responses via latent heat exchange, freshwater redistribution, and the rate and efficiency of local heat uptake. Globally integrated, the OHU efficiency is as high as the climate feedback parameter for more than a decade. Since the oceanic adjustment involves surface heat fluxes, differentiating between time scales of adjustment and feedbacks is even more convoluted than in the atmosphere. We conclude that analysing the ocean's role is necessary to quantify a forcing's short time scale contribution to transient and equilibrium climate sensitivity because of (1) the oceans' impact on the magnitude of the atmospheric adjustment and (2) the initially very high OHU efficiency.

  5. Exceptional ocean surface conditions on the SE Greenland shelf during the Medieval Climate Anomaly

    NASA Astrophysics Data System (ADS)

    Miettinen, Arto; Divine, Dmitry V.; Husum, Katrine; Koç, Nalan; Jennings, Anne

    2015-12-01

    Diatom inferred 2900 year long records of August sea surface temperature (aSST) and April sea ice concentration (aSIC) are generated from a marine sediment core from the SE Greenland shelf with a special focus on the interval ca. 870-1910 Common Era (C.E.) reconstructed in subdecadal temporal resolution. The Medieval Climate Anomaly (MCA) between 1000 and 1200 C.E. represents the warmest ocean surface conditions of the SE Greenland shelf over the late Holocene (880 B.C.E.(before the Common Era) to 1910 C.E.). It was characterized by abrupt, decadal to multidecadal changes, such as an abrupt warming of ~2.4°C in 55 years around 1000 C.E. Temperature changes of these magnitudes are rare on the North Atlantic proxy data. Compared to regional air temperature reconstructions, our results indicate a lag of about 50 years in ocean surface warming either due to increased freshwater discharge from the Greenland ice sheet or intensified sea ice export from the Arctic as a response to atmospheric warming at the beginning of the MCA. A cool phase, from 1200-1890 C.E., associated with the Little Ice Age, ends with the rapid warming of aSST and diminished aSIC in the early twentieth century. The results show that the periods of warm aSST and aSIC minima are coupled with solar minima suggesting that solar forcing possibly amplified by atmospheric forcing have been behind the variability of surface conditions on the SE Greenland over the last millennium. The results indicate that the SE Greenland shelf is a climatologically sensitive area where extremely rapid changes are possible and highlights the importance of the area under the present warming conditions.

  6. Modulation of Saharan dust export by the North African dipole

    NASA Astrophysics Data System (ADS)

    Rodríguez, S.; Cuevas, E.; Prospero, J. M.; Alastuey, A.; Querol, X.; López-Solano, J.; García, M. I.; Alonso-Pérez, S.

    2014-10-01

    Desert dust aerosols influence air quality and climate on a global scale, including radiative forcing, cloud properties and carbon dioxide modulation through ocean fertilisation. North Africa is the largest and most active dust source worldwide; however, the mechanisms modulating year-to-year variability in Saharan dust export in summer remains unclear. In this season, enhanced dust mobilization in the hyper-arid Sahara results in maximum dust impacts throughout the North Atlantic. The objective of this study is to identify the relationship between the long term interannual variability in Saharan dust export in summer and large scale meteorology in western North Africa. We address this issue by analysing ~25 yr (1987-2012) dust concentrations at the high altitude Izaña observatory (2373 m a.s.l.) in Tenerife Island, satellite and meteorological reanalysis data. Because in summer Saharan dust export occurs at altitudes 1-5 km, we paid special attention to the summer meteorological scenario in the 700 hPa standard level, characterised by a high over the subtropical Sahara and lower geopotential heights over the tropics; we measured the intensity of this low-high dipole like pattern in terms of the North AFrican Dipole Index (NAFDI): the difference of the 700 hPa geopotential heights anomalies averaged over central Morocco (subtropic) and over Bamako region (tropic). The correlations we found between the 1987-2012 NAFDI with dust at Izaña, satellite dust observations and meteorological re-analysis data, indicates that increase in the NAFDI (i) results in higher wind speeds at the north of the Inter-Tropical Convergence Zone which enhances dust export over the subtropical North Atlantic, (ii) influences on the size distribution of exported dust particles, increasing the load of coarse dust and (iii) are associated with higher rainfall over tropical North Africa and the Sahel. Because of the North African dipole modulation, inter-annual variability in Saharan dust export is correlated with monsoon rainfall in the Sahel. High values of the NAFDI enhance dust export at subtropical latitudes. Our results suggest that long term variability in Saharan dust export may be influenced by global oscillations in the climate of the tropics and subtropics and that this may have influenced dust transport pathways in the last decades.

  7. Arctic Ocean

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.; Zukor, Dorothy J. (Technical Monitor)

    2000-01-01

    The Arctic Ocean is the smallest of the Earth's four major oceans, covering 14x10(exp 6) sq km located entirely within the Arctic Circle (66 deg 33 min N). It is a major player in the climate of the north polar region and has a variable sea ice cover that tends to increase its sensitivity to climate change. Its temperature, salinity, and ice cover have all undergone changes in the past several decades, although it is uncertain whether these predominantly reflect long-term trends, oscillations within the system, or natural variability. Major changes include a warming and expansion of the Atlantic layer, at depths of 200-900 m, a warming of the upper ocean in the Beaufort Sea, a considerable thinning (perhaps as high as 40%) of the sea ice cover, a lesser and uneven retreat of the ice cover (averaging approximately 3% per decade), and a mixed pattern of salinity increases and decreases.

  8. Role of the Freshwater Forcing on the Atlantic Thermohaline Circulation in Climate Changes

    NASA Astrophysics Data System (ADS)

    Murakami, S.; Kitoh, A.

    2005-12-01

    Effects of the freshwater forcing changes on the thermohaline circulation (THC) differ depending on as to which regimes the circulation is in. This fact is obvious from the considerations based on the simple conceptual box models like Stommel 1961 or Rahmstorf 1996. However, the THC regime of the real Atlantic is not obvious including the problem as to whether such a simple view is applicable or not. In this study, the authors try to determine the Atlantic THC regime of the MRI-CGCM2 from an analysis of a partially coupled experiment, where the greenhouse gas concentrations are fixed to the present-day values but the ocean surface freshwater flux is taken from a transient global warming experiment. Such an experiment is thought to show the role of freshwater forcing more clearly then a fully coupled transient global warming simulation. Analyses show that the salt content of the northern North Atlantic increases in the case of global warming as a long-term response although the water flux over there makes the surface water fresher. It stabilize (or enhance) the Atlantic THC as a long-term response. This response of the THC to an increased freshwater forcing suggests that the THC of the MRI-CGCM2 is in the thermohaline driven regime in the context of the boxmodels. The freshwater flux adjustment used in the MRI-CGCM2 make the problem somewhat complicated. However, a consideration based on the box model and the Atlantic freshwater budget suggests that this result can be generalized to other AOGCMs and/or the real world.

  9. New insights into the organic carbon export in the Mediterranean Sea from 3-D modeling

    NASA Astrophysics Data System (ADS)

    Guyennon, A.; Baklouti, M.; Diaz, F.; Palmieri, J.; Beuvier, J.; Lebaupin-Brossier, C.; Arsouze, T.; Béranger, K.; Dutay, J.-C.; Moutin, T.

    2015-12-01

    The Mediterranean Sea is one of the most oligotrophic regions of the oceans, and nutrients have been shown to limit both phytoplankton and bacterial activities, resulting in a potential major role of dissolved organic carbon (DOC) export in the biological pump. Strong DOC accumulation in surface waters is already well documented, though measurements of DOC stocks and export flux are still sparse and associated with major uncertainties. This study provides the first basin-scale overview and analysis of organic carbon stocks and export fluxes in the Mediterranean Sea through a modeling approach based on a coupled model combining a mechanistic biogeochemical model (Eco3M-MED) and a high-resolution (eddy-resolving) hydrodynamic simulation (NEMO-MED12). The model is shown to reproduce the main spatial and seasonal biogeochemical characteristics of the Mediterranean Sea. Model estimations of carbon export are also of the same order of magnitude as estimations from in situ observations, and their respective spatial patterns are mutually consistent. Strong differences between the western and eastern basins are evidenced by the model for organic carbon export. Though less oligotrophic than the eastern basin, the western basin only supports 39 % of organic carbon (particulate and dissolved) export. Another major result is that except for the Alboran Sea, the DOC contribution to organic carbon export is higher than that of particulate organic carbon (POC) throughout the Mediterranean Sea, especially in the eastern basin. This paper also investigates the seasonality of DOC and POC exports as well as the differences in the processes involved in DOC and POC exports in light of intracellular quotas. Finally, according to the model, strong phosphate limitation of both bacteria and phytoplankton growth is one of the main drivers of DOC accumulation and therefore of export.

  10. Fram Strait Sea Ice Volume Export 1992-2012 from Combined ULS and Satellite Data

    NASA Astrophysics Data System (ADS)

    Spreen, G.; Hansen, E.; Kwok, R.; Gerland, S.

    2013-12-01

    The Fram Strait between Svalbard and Greenland is the main gateway for sea ice export out of the Arctic Basin. Changes of the sea ice mass balance can either have thermodynamic (melting) or dynamic (export) causes, or a combination of both. Therefore, to better understand the recent decrease in Arctic sea ice volume it is of special importance to monitor changes in the sea ice export. Additionally, inter-annual perturbations in the sea ice transport through Fram Strait can modify the major water mass formation processes in the Greenland Sea and further downstream with consequences for the deep water formation and global ocean circulation. To estimate the sea ice volume export through Fram Strait the three variables sea ice drift, area, and thickness have to be known and combined. The long-term Fram Strait sea ice area export obtained from passive microwave satellite observations since 1982 shows no significant trend. However, for the last decade 2001-2009 a positive trend in sea ice area export can be observed. The sea ice thickness in Fram Strait at 79N is monitored by Upward Looking Sonars (ULS) since 1990. A newly reprocessed and extended ULS time series for 1990-2011 shows negative ice thickness trends of about 3 and 5 cm per year for the mean and modal ice thickness, respectively, with an increasing negative trend since about 2003. For the combined sea ice volume export some of this reduced ice thickness may compensate the increased ice area export in recent years. We will present an updated Fram Strait sea ice volume export time series for the period 1992 to 2012, combining in-situ ULS ice thickness data with satellite passive microwave observations of sea ice drift and area. Long-term and decadal changes of the ice export are discussed in context with the recent sea ice area and volume decrease in the Arctic Basin.

  11. EFFECTS OF POLLUTION ON FRESHWATER FISH

    EPA Science Inventory

    An extensive literature review is presented which is concerned with the effects of pollutants (metals, pesticides, detergents, industrial wastes) on freshwater fish; chemical and biological methods for identifying and determining the effects of such pollutants; and the effects of...

  12. Best Management Practices for Freshwater Pond Aquaculture

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This chapter in the book Environmental Best Management Practices for Aquaculture describes freshwater pond aquaculture systems and management practices to reduce environmental impacts of pond aquaculture. Pond aquaculture systems for channel catfish, crawfish, baitfish, hybrid striped bass, and o...

  13. Fluid flow enhances the effectiveness of toxin export by aquatic microorganisms: a first-passage perspective

    NASA Astrophysics Data System (ADS)

    Licata, Nicholas; Clark, Aaron

    2014-03-01

    Aquatic microorganisms face a variety of challenges in the course of development. One central challenge is efficiently regulating the export of toxic molecules inside the developing embryo. The strategies employed should be robust with respect to the variable ocean environment and limit the chances that exported toxins are reabsorbed. In this talk we consider the first-passage problem for the uptake of exported toxins by a spherical embryo. A perturbative solution of the advection-diffusion equation reveals that a concentration boundary layer forms in the vicinity of the embryo, and that fluid flow enhances the effectiveness of toxin export. We highlight connections between the model results and recent experiments on the development of sea urchin embryos. We acknowledge financial support from the University of Michigan-Dearobrn CASL Faculty Summer Research Grant.

  14. A decrease in discharge-normalized DOC export by the Yukon River during summer through autumn

    USGS Publications Warehouse

    Striegl, R.G.; Aiken, G.R.; Dornblaser, M.M.; Raymond, P.A.; Wickland, K.P.

    2005-01-01

    Climate warming is having a dramatic effect on the vegetation distribution and carbon cycling of terrestrial subarctic and arctic ecosystems. Here, we present hydrologic evidence that warming is also affecting the export of dissolved organic carbon and bicarbonate (DOC and HCO3-) at the large basin scale. In the 831,400 km2 Yukon River basin, water discharge (Q) corrected DOC export significantly decreased during the growing season from 1978-80 to 2001-03, indicating a major shift in terrestrial to aquatic C transfer. We conclude that decreased DOC export, relative to total summer through autumn Q, results from increased flow path, residence time, and microbial mineralization of DOC in the soil active layer and groundwater. Counter to current predictions, we argue that continued warming could result in decreased DOC export to the Bering Sea and Arctic Ocean by major subarctic and arctic rivers, due to increased respiration of organic C on land. Copyright 2005 by the American Geophysical Union.

  15. A Freshwater Starvation Mechanism for Dansgaard-Oeschger Cycles

    NASA Astrophysics Data System (ADS)

    Wolff, E. W.; Hewitt, I.; Fowler, A.; Clark, C.; Evatt, G. W.; Munday, D. R.; Stokes, C.

    2014-12-01

    Many northern hemisphere climate records, particularly those from around the North Atlantic, show a series of rapid climate changes that recurred on centennial to millennial timescales throughout most of the last glacial period. These Dansgaard-Oeschger (D-O) sequences are observed most prominently in Greenland ice cores, although they have a global signature, including an out of phase Antarctic signal. They consist of warming jumps of order 10C, occurring in typically 40 years, followed generally by a slow cooling (Greenland Interstadial, GI) lasting between a few centuries and a few millennia, and then a final rapid temperature drop into a cold Greenland Stadial (GS) that lasts for a similar period. The most distinctive feature of D-O cycles is the rapid warming event, often attributed to a sudden change in the strength of the Atlantic meridional overturning circulation (AMOC). Recent work has suggested that AMOC is most easily disrupted by freshwater delivered through the Arctic. We suggest that the proposed AMOC changes may have occurred as part of a natural oscillation, in which runoff from the Laurentide ice sheet into the Arctic is controlled by temperature around the North Atlantic. The Arctic buffers the salinity changes, but under warm conditions, high runoff eventually leads to water entering the North Atlantic with low enough salinity to switch AMOC into its weaker state. Under the colder conditions now prevailing, the Arctic is starved of runoff, and the salinity rises until a further switch occurs. Contrary to many previous studies, this mechanism does not require large freshwater pulses to the North Atlantic. Instead, steady changes in ice-sheet runoff, driven by the AMOC, lead to a naturally arising oscillator, in which the rapid warmings come about because the Arctic Ocean is starved of freshwater. The changing size of the ice sheets would have affected the magnitude and extent of runoff, and we suggest that this may provide a simple explanation for the absence of the events during interglacials and around the time of glacial maxima. Heinrich events, delivering additional freshwater into the Atlantic during a Greenland stadial, play no direct role in this mechanism, but would serve to delay the switch to faster AMOC.

  16. Long-term ocean simulations in FESOM: evaluation and application in studying the impact of Greenland Ice Sheet melting

    NASA Astrophysics Data System (ADS)

    Wang, Xuezhu; Wang, Qiang; Sidorenko, Dmitry; Danilov, Sergey; Schrter, Jens; Jung, Thomas

    2012-12-01

    The Finite Element Sea-ice Ocean Model (FESOM) is formulated on unstructured meshes and offers geometrical flexibility which is difficult to achieve on traditional structured grids. In this work, the performance of FESOM in the North Atlantic and Arctic Ocean on large time scales is evaluated in a hindcast experiment. A water-hosing experiment is also conducted to study the model sensitivity to increased freshwater input from Greenland Ice Sheet (GrIS) melting in a 0.1-Sv discharge rate scenario. The variability of the Atlantic Meridional Overturning Circulation (AMOC) in the hindcast experiment can be explained by the variability of the thermohaline forcing over deep convection sites. The model also reproduces realistic freshwater content variability and sea ice extent in the Arctic Ocean. The anomalous freshwater in the water-hosing experiment leads to significant changes in the ocean circulation and local dynamical sea level (DSL). The most pronounced DSL rise is in the northwest North Atlantic as shown in previous studies, and also in the Arctic Ocean. The released GrIS freshwater mainly remains in the North Atlantic, Arctic Ocean and the west South Atlantic after 120 model years. The pattern of ocean freshening is similar to that of the GrIS water distribution, but changes in ocean circulation also contribute to the ocean salinity change. The changes in Arctic and sub-Arctic sea level modify exchanges between the Arctic Ocean and subpolar seas, and hence the role of the Arctic Ocean in the global climate. Not only the strength of the AMOC, but also the strength of its decadal variability is notably reduced by the anomalous freshwater input. A comparison of FESOM with results from previous studies shows that FESOM can simulate past ocean state and the impact of increased GrIS melting well.

  17. Enhanced deep ocean ventilation and oxygenation with global warming

    NASA Astrophysics Data System (ADS)

    Froelicher, T. L.; Jaccard, S.; Dunne, J. P.; Paynter, D.; Gruber, N.

    2014-12-01

    Twenty-first century coupled climate model simulations, observations from the recent past, and theoretical arguments suggest a consistent trend towards warmer ocean temperatures and fresher polar surface oceans in response to increased radiative forcing resulting in increased upper ocean stratification and reduced ventilation and oxygenation of the deep ocean. Paleo-proxy records of the warming at the end of the last ice age, however, suggests a different outcome, namely a better ventilated and oxygenated deep ocean with global warming. Here we use a four thousand year global warming simulation from a comprehensive Earth System Model (GFDL ESM2M) to show that this conundrum is a consequence of different rates of warming and that the deep ocean is actually better ventilated and oxygenated in a future warmer equilibrated climate consistent with paleo-proxy records. The enhanced deep ocean ventilation in the Southern Ocean occurs in spite of increased positive surface buoyancy fluxes and a constancy of the Southern Hemisphere westerly winds - circumstances that would otherwise be expected to lead to a reduction in deep ocean ventilation. This ventilation recovery occurs through a global scale interaction of the Atlantic Meridional Overturning Circulation undergoing a multi-centennial recovery after an initial century of transient decrease and transports salinity-rich waters inform the subtropical surface ocean to the Southern Ocean interior on multi-century timescales. The subsequent upwelling of salinity-rich waters in the Southern Ocean strips away the freshwater cap that maintains vertical stability and increases open ocean convection and the formation of Antarctic Bottom Waters. As a result, the global ocean oxygen content and the nutrient supply from the deep ocean to the surface are higher in a warmer ocean. The implications for past and future changes in ocean heat and carbon storage will be discussed.

  18. Freshwater Commercial Bycatch: an Understated Conservation Problem

    SciTech Connect

    Raby, Graham D.; Colotelo, Alison HA; Blouin-Demers, Gabriel; Cooke, Steven J.

    2011-04-01

    Commercial fisheries bycatch in marine systems has been regarded as a global conservation concern by environmental groups, scientists, government, and the public for decades. Fortunately, some headway has been made to mitigate the negative impacts of bycatch in marine environments. In a survey of the literature, we found that despite freshwater commercial fisheries yields comprising 11% of the global commercial catch, bycatch research focusing on freshwater commercial fisheries represented only {approx}3% of the total bycatch literature. This paucity of research is particularly alarming given that freshwater animals and habitats are some of the world's most imperiled. The limited inland bycatch literature that does exist includes examples of population declines attributed to commercial bycatch (e.g., freshwater dolphins in the Yangtze River in China) and illustrates that in some systems bycatch can be substantial (e.g., lake trout bycatch in the Laurentian Great Lakes). Encouraging results from the marine realm can serve as models for bycatch research in freshwater, and lead to measurable gains in conservation of freshwater ecosystems. We summarize existing work on inland bycatch in an effort to draw attention to this understated and understudied conservation problem.

  19. 78 FR 31517 - Export Trade Certificate of Review

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-05-24

    ... Export Trade Certificate of Review to California Almond Export Association, LLC (``CAEA'') (Application... Review to California Almond Export Association, LLC on May 20, 2013. FOR FURTHER INFORMATION...

  20. The imbalance of new and export production in the western Antarctic Peninsula, a potentially "leaky" ecosystem

    NASA Astrophysics Data System (ADS)

    Stukel, Michael R.; Asher, Elizabeth; Couto, Nicole; Schofield, Oscar; Strebel, Stefanie; Tortell, Philippe; Ducklow, Hugh W.

    2015-09-01

    To quantify the balance between new production and vertical nitrogen export of sinking particles, we measured nitrate uptake, net nitrate drawdown, ΔO2/Ar-based net community production, sediment trap flux, and 234Th export at a coastal site near Palmer Station, Antarctica, during the phytoplankton growing season from October 2012 to March 2013. We also measured nitrate uptake and 234Th export throughout the northern western Antarctic Peninsula (WAP) region on a cruise in January 2013. We used a nonsteady state 234Th equation with temporally varying upwelling rates and an irradiance-based phytoplankton production model to correct our export and new production estimates in the complex coastal site near Palmer Station. Results unequivocally showed that nitrate uptake and net community production were significantly greater than the sinking particle export on region-wide spatial scales and season-long temporal scales. At our coastal site, new production (105 ± 17.4 mg N m-2 d-1, mean ± standard error) was 5.3 times greater than vertical nitrogen export (20.4 ± 2.4 mg N m-2 d-1). On the January cruise in the northern WAP, new production (47.9 ± 14.4 mg N m-2 d-1) was 2.4 times greater than export (19.9 ± 1.4 mg N m-2 d-1). Much of this imbalance can be attributed to diffusive losses of particulate nitrogen from the surface ocean due to diapycnal mixing, indicative of a "leaky" WAP ecosystem. If these diffusive losses are common in other systems where new production exceeds export, it may be necessary to revise current estimates of the ocean's biological pump.

  1. Climate Change-Related Hydrologic Variation Affects Dissolved Organic Carbon Export to the Gulf of Maine

    NASA Astrophysics Data System (ADS)

    Huntington, T. G.; Balch, W. M.; Aiken, G.; Butler, K. D.; Billmire, M.; Roesler, C. S.; Camill, P.; Bourakovsky, A.

    2014-12-01

    Ongoing climate change is affecting the timing and amount of dissolved organic carbon (DOC) exported to the Gulf of Maine (GoM) through effects on hydrologic conditions. Climate warming in the northeast United States has resulted in decreases in snowfall amount and increases in the proportion of annual precipitation that falls as rain compared with snow. Warming has resulted in an increase in runoff during winter and earlier snowmelt and associated high spring flow. Increases in annual precipitation have resulted in increases in annual runoff. Increases in flashiness in some rivers have resulted in higher variability in daily runoff. DOC fluxes were estimated for water years 1950 through 2012 in eight rivers draining to the GoM that had long-term discharge data and data for DOC during all months of the year. These estimates used LOADEST to fit a seasonally-adjusted concentration - discharge relation. The adjusted maximum likelihood estimation (AMLE) method was used to estimate loads. One of several predefined regression models evaluated in LOADEST was selected based on the Akaike information criterion (AIC) for each river. This analysis assumed stationarity in the concentration - discharge relations. The proportion of total annual DOC exported during winter has increased. The proportion of DOC exported during March and April has also increased and the proportion exported during May has decreased in association with earlier snowmelt runoff and earlier recession to summer low flow. The total annual DOC exported by these rivers increased significantly from 1950 to 2012. The increase in flashiness has increased daily variability in DOC export in some rivers. Changes in the timing and amount of DOC exported to the near coastal ocean may influence marine biogeochemistry including the development of nuisance and harmful algal blooms, carbon sequestration, and the interpretation of satellite-derived ocean color. Terrestrially derived DOC exported to the marine environment could decrease phytoplankton productivity through light attenuation.

  2. Ocean bowling

    NASA Astrophysics Data System (ADS)

    Showstack, Randy

    Coach Scott Carpenter, a biology teacher at Lexington High School in Massachusetts, says that some [students] want to show that they can win on a football field, and some want to show that they know science better than anyone else.His team of four sophomores and one senior proved their mettle when they won the 1998 National Ocean Science Bowl on April 27.

  3. The Ocean.

    ERIC Educational Resources Information Center

    Broecker, Wallace S.

    1983-01-01

    The chemistry of the ocean, whose constituents interact with those of air and land to support life and influence climate, is known to have undergone changes since the last glacial epoch. Changes in dissolved oxygen, calcium ions, phosphate, carbon dioxide, carbonate ions, and bicarbonate ions are discussed. (JN)

  4. Commissioned Review. Carbon: freshwater plants

    USGS Publications Warehouse

    Keeley, J.E.; Sandquist, D.R.

    1992-01-01

    δ13C values for freshwater aquatic plant matter varies from −11 to −50‰ and is not a clear indicator of photosynthetic pathway as in terrestrial plants. Several factors affect δ13C of aquatic plant matter. These include: (1) The δ13C signature of the source carbon has been observed to range from +1‰ for HCO3− derived from limestone to −30‰ for CO2 derived from respiration. (2) Some plants assimilate HCO3−, which is –7 to –11‰ less negative than CO2. (3) C3, C4, and CAM photosynthetic pathways are present in aquatic plants. (4) Diffusional resistances are orders of magnitude greater in the aquatic environment than in the aerial environment. The greater viscosity of water acts to reduce mixing of the carbon pool in the boundary layer with that of the bulk solution. In effect, many aquatic plants draw from a finite carbon pool, and as in terrestrial plants growing in a closed system, biochemical discrimination is reduced. In standing water, this factor results in most aquatic plants having a δ13C value similar to the source carbon. Using Farquhar's equation and other physiological data, it is possible to use δ13C values to evaluate various parameters affecting photosynthesis, such as limitations imposed by CO2 diffusion and carbon source.

  5. Natural Gas Exports from Iran

    EIA Publications

    2012-01-01

    This assessment of the natural gas sector in Iran, with a focus on Iran’s natural gas exports, was prepared pursuant to section 505 (a) of the Iran Threat Reduction and Syria Human Rights Act of 2012 (Public Law No: 112-158). As requested, it includes: (1) an assessment of exports of natural gas from Iran; (2) an identification of the countries that purchase the most natural gas from Iran; (3) an assessment of alternative supplies of natural gas available to those countries; (4) an assessment of the impact a reduction in exports of natural gas from Iran would have on global natural gas supplies and the price of natural gas, especially in countries identified under number (2); and (5) such other information as the Administrator considers appropriate.

  6. Export production fluctuations in the eastern equatorial Pacific during the Pliocene-Pleistocene: Reconstruction using barite accumulation rates

    NASA Astrophysics Data System (ADS)

    Ma, Zhongwu; Ravelo, Ana Christina; Liu, Zhonghui; Zhou, Liping; Paytan, Adina

    2015-11-01

    Export production is an important component of the carbon cycle, modulating the climate system by transferring CO2 from the atmosphere to the deep ocean via the biological pump. Here we use barite accumulation rates to reconstruct export production in the eastern equatorial Pacific over the past 4.3 Ma. We find that export production fluctuated considerably on multiple time scales. Export production was on average higher (51 g C m-2 yr-1) during the Pliocene than the Pleistocene (40 g C m-2 yr-1), decreasing between 3 and 1 Ma (from more than 60 to 20 g C m-2 yr-1) followed by an increase over the last million years. These trends likely reflect basin-scale changes in nutrient inventory and ocean circulation. Our record reveals decoupling between export production and temperatures on these long (million years) time scale. On orbital time scales, export production was generally higher during cold periods (glacial maxima) between 4.3 and 1.1 Ma. This could be due to stronger wind stress and higher upwelling rates during glacial periods. A shift in the timing of maximum export production to deglaciations is seen in the last ~1.1 million years. Results from this study suggest that, in the eastern equatorial Pacific, mechanisms that affect nutrient supply and/or ecosystem structure and in turn carbon export on orbital time scales differ from those operating on longer time scales and that processes linking export production and climate-modulated oceanic conditions changed about 1.1 million years ago. These observations should be accounted for in climate models to ensure better predictions of future climate change.

  7. Global carbon export from the terrestrial biosphere controlled by erosion.

    PubMed

    Galy, Valier; Peucker-Ehrenbrink, Bernhard; Eglinton, Timothy

    2015-05-14

    Riverine export of particulate organic carbon (POC) to the ocean affects the atmospheric carbon inventory over a broad range of timescales. On geological timescales, the balance between sequestration of POC from the terrestrial biosphere and oxidation of rock-derived (petrogenic) organic carbon sets the magnitude of the atmospheric carbon and oxygen reservoirs. Over shorter timescales, variations in the rate of exchange between carbon reservoirs, such as soils and marine sediments, also modulate atmospheric carbon dioxide levels. The respective fluxes of biospheric and petrogenic organic carbon are poorly constrained, however, and mechanisms controlling POC export have remained elusive, limiting our ability to predict POC fluxes quantitatively as a result of climatic or tectonic changes. Here we estimate biospheric and petrogenic POC fluxes for a suite of river systems representative of the natural variability in catchment properties. We show that export yields of both biospheric and petrogenic POC are positively related to the yield of suspended sediment, revealing that POC export is mostly controlled by physical erosion. Using a global compilation of gauged suspended sediment flux, we derive separate estimates of global biospheric and petrogenic POC fluxes of 157(+74)(-50) and 43(+61)(-25) megatonnes of carbon per year, respectively. We find that biospheric POC export is primarily controlled by the capacity of rivers to mobilize and transport POC, and is largely insensitive to the magnitude of terrestrial primary production. Globally, physical erosion rates affect the rate of biospheric POC burial in marine sediments more strongly than carbon sequestration through silicate weathering. We conclude that burial of biospheric POC in marine sediments becomes the dominant long-term atmospheric carbon dioxide sink under enhanced physical erosion. PMID:25971513

  8. Global carbon export from the terrestrial biosphere controlled by erosion

    NASA Astrophysics Data System (ADS)

    Galy, Valier; Peucker-Ehrenbrink, Bernhard; Eglinton, Timothy

    2015-05-01

    Riverine export of particulate organic carbon (POC) to the ocean affects the atmospheric carbon inventory over a broad range of timescales. On geological timescales, the balance between sequestration of POC from the terrestrial biosphere and oxidation of rock-derived (petrogenic) organic carbon sets the magnitude of the atmospheric carbon and oxygen reservoirs. Over shorter timescales, variations in the rate of exchange between carbon reservoirs, such as soils and marine sediments, also modulate atmospheric carbon dioxide levels. The respective fluxes of biospheric and petrogenic organic carbon are poorly constrained, however, and mechanisms controlling POC export have remained elusive, limiting our ability to predict POC fluxes quantitatively as a result of climatic or tectonic changes. Here we estimate biospheric and petrogenic POC fluxes for a suite of river systems representative of the natural variability in catchment properties. We show that export yields of both biospheric and petrogenic POC are positively related to the yield of suspended sediment, revealing that POC export is mostly controlled by physical erosion. Using a global compilation of gauged suspended sediment flux, we derive separate estimates of global biospheric and petrogenic POC fluxes of and megatonnes of carbon per year, respectively. We find that biospheric POC export is primarily controlled by the capacity of rivers to mobilize and transport POC, and is largely insensitive to the magnitude of terrestrial primary production. Globally, physical erosion rates affect the rate of biospheric POC burial in marine sediments more strongly than carbon sequestration through silicate weathering. We conclude that burial of biospheric POC in marine sediments becomes the dominant long-term atmospheric carbon dioxide sink under enhanced physical erosion.

  9. Sixth Australian conference on coastal and ocean engineering (Preprints)

    SciTech Connect

    Not Available

    1983-01-01

    This book presents the papers given at a conference on marine engineering. Topics considered at the conference included wave measurements and the utilization of wave data, field studies of currents and simulation of oil dispersion in the Central Great Barrier Reef, a practical method for determining the dispersion at an ocean outfall, water level variations in aquifers caused by ocean tides, and design procedures and parameters for marine facilities at coal export terminals.

  10. Controlling high-latitude Southern Ocean convection in climate models

    NASA Astrophysics Data System (ADS)

    Stssel, Achim; Notz, Dirk; Haumann, F. Alexander; Haak, Helmuth; Jungclaus, Johann; Mikolajewicz, Uwe

    2015-02-01

    Earth System Models (ESMs) generally suffer from a poor simulation of the High-Latitude Southern Ocean (HLSO). Here we aim at a better understanding of the shortcomings by investigating the sensitivity of the HLSO to the external freshwater flux and the horizontal resolution in forced and coupled simulations with the Max-Planck-Institute Ocean Model (MPIOM). Forced experiments reveal an immediate reduction of open-ocean convection with additional freshwater input. The latter leads to a remarkably realistic simulation of the distinct water-mass structure in the central Weddell Sea featuring a temperature maximum of +0.5 C at 250 m depth. Similar, but more modest improvements occur over a time span of 40 years after switching from a forced to a coupled simulation with an eddy-resolving version of MPIOM. The switch is accompanied with pronounced changes of the external freshwater flux and the wind field, as well as a more realistic heat flux due to coupling. Similar to the forced freshwater-flux experiments, a heat reservoir develops at depth, which in turn decreases the vertically integrated density of the HLSO and reduces the Antarctic Circumpolar Current to rather realistic values. Coupling with a higher resolution version of the atmosphere model (ECHAM6) yields distinct improvements of the HLSO water-mass structure and sea-ice cover. While the coupled simulations reveal a realistic amount of Antarctic runoff, its distribution appears too concentrated along the coast. Spreading the runoff over a wider region, as suggested in earlier studies to mimic the effect of freshwater transport through icebergs, also leads to noticeable improvements of the HLSO water-mass properties, predominantly along the coast. This suggests that the spread of the runoff improves the representation of Antarctic Bottom Water formation through enhanced near-boundary convection rather than weakened open-ocean convection.

  11. Model Sensitivity to North Atlantic Freshwater Forcing at 8.2 Ka

    NASA Technical Reports Server (NTRS)

    Morrill, Carrie; Legrande, Allegra Nicole; Renssen, H.; Bakker, P.; Otto-Bliesner, B. L.

    2013-01-01

    We compared four simulations of the 8.2 ka event to assess climate model sensitivity and skill in responding to North Atlantic freshwater perturbations. All of the simulations used the same freshwater forcing, 2.5 Sv for one year, applied to either the Hudson Bay (northeastern Canada) or Labrador Sea (between Canada's Labrador coast and Greenland). This freshwater pulse induced a decadal-mean slowdown of 10-25%in the Atlantic Meridional Overturning Circulation (AMOC) of the models and caused a large-scale pattern of climate anomalies that matched proxy evidence for cooling in the Northern Hemisphere and a southward shift of the Intertropical Convergence Zone. The multi-model ensemble generated temperature anomalies that were just half as large as those from quantitative proxy reconstructions, however. Also, the duration of AMOC and climate anomalies in three of the simulations was only several decades, significantly shorter than the duration of approx.150 yr in the paleoclimate record. Possible reasons for these discrepancies include incorrect representation of the early Holocene climate and ocean state in the North Atlantic and uncertainties in the freshwater forcing estimates.

  12. The molecular phylogeny of freshwater Dothideomycetes

    PubMed Central

    Shearer, C.A.; Raja, H.A.; Miller, A.N.; Nelson, P.; Tanaka, K.; Hirayama, K.; Marvanov, L.; Hyde, K.D.; Zhang, Y.

    2009-01-01

    The freshwater Dothideomycetes species are an ecological rather than taxonomic group and comprise approximately 178 meiosporic and mitosporic species. Due to convergent or parallel morphological adaptations to aquatic habitats, it is difficult to determine phylogenetic relationships among freshwater taxa and among freshwater, marine and terrestrial taxa based solely on morphology. We conducted molecular sequence-based phylogenetic analyses using nuclear ribosomal sequences (SSU and/or LSU) for 84 isolates of described and undescribed freshwater Dothideomycetes and 85 additional taxa representative of the major orders and families of Dothideomycetes. Results indicated that this ecological group is not monophyletic and all the freshwater taxa, except three aeroaquatic Tubeufiaceae, occur in Pleosporomycetidae as opposed to Dothideomycetidae. Four clades comprised of only freshwater taxa were recovered. The largest of these is the Jahnulales clade consisting of 13 species, two of which are the anamorphs Brachiosphaera tropicalis and Xylomyces chlamydosporus. The second most speciose clade is the Lindgomycetaceae clade consisting of nine taxa including the anamorph Taeniolella typhoides. The Lindgomycetaceae clade consists of taxa formerly described in Massarina, Lophiostoma, and Massariosphaeria e.g., Massarina ingoldiana, Lophiostoma breviappendiculatum, and Massariosphaeria typhicola and several newly described and undescribed taxa. The aquatic family Amniculicolaceae, including three species of Amniculicola, Semimassariosphaeria typhicola and the anamorph, Anguillospora longissima, was well supported. A fourth clade of freshwater species consisting of Tingoldiago graminicola, Lentithecium aquaticum, L. arundinaceum and undescribed taxon A-369-2b was not well supported with maximum likelihood bootstrap and Bayesian posterior probability. Eight freshwater taxa occurred along with terrestrial species in the Lophiostoma clades 1 and 2. Two taxa lacking statistical support for their placement with any taxa included in this study are considered singletons within Pleosporomycetidae. These singletons, Ocala scalariformis, and Lepidopterella palustris, are morphologically distinct from other taxa in Pleosporomycetidae. This study suggests that freshwater Dothideomycetes are related to terrestrial taxa and have adapted to freshwater habitats numerous times. In some cases (Jahnulales and Lindgomycetaceae), species radiation appears to have occurred. Additional collections and molecular study are required to further clarify the phylogeny of this interesting ecological group. PMID:20169028

  13. Tidal day organic and inorganic material flux of ponds in the Liberty Island freshwater tidal wetland.

    PubMed

    Lehman, Peggy W; Mayr, Shawn; Liu, Leji; Tang, Alison

    2015-01-01

    The loss of inorganic and organic material export and habitat produced by freshwater tidal wetlands is hypothesized to be an important contributing factor to the long-term decline in fishery production in San Francisco Estuary. However, due to the absence of freshwater tidal wetlands in the estuary, there is little information on the export of inorganic and organic carbon, nutrient or phytoplankton community biomass and the associated mechanisms. A single-day study was conducted to assess the potential contribution of two small vegetated ponds and one large open-water pond to the inorganic and organic material flux within the freshwater tidal wetland Liberty Island in San Francisco Estuary. The study consisted of an intensive tidal day (25.5h) sampling program that measured the flux of inorganic and organic material at three ponds using continuous monitoring of flow, chlorophyll a, turbidity and salt combined with discrete measurements of phytoplankton community carbon, total and dissolved organic carbon and nutrient concentration at 1.5h intervals. Vegetated ponds had greater material concentrations than the open water pond and, despite their small area, contributed up to 81% of the organic and 61% of the inorganic material flux of the wetland. Exchange between ponds was important to wetland flux. The small vegetated pond in the interior of the wetland contributed as much as 72-87% of the total organic carbon and chlorophyll a and 10% of the diatom flux of the wetland. Export of inorganic and organic material from the small vegetated ponds was facilitated by small-scale topography and tidal asymmetry that produced a 40% greater material export on ebb tide. The small vegetated ponds contrasted with the large open water pond, which imported 29-96% of the inorganic and 4-81% of the organic material into the wetland from the adjacent river. This study identified small vegetated ponds as an important source of inorganic and organic material to the wetland and the importance of small scale physical processes within ponds to material flux of the wetland. PMID:26090320

  14. Fennoscandian freshwater control on Greenland hydroclimate shifts at the onset of the Younger Dryas

    NASA Astrophysics Data System (ADS)

    Muschitiello, Francesco; Pausata, Francesco S. R.; Watson, Jenny E.; Smittenberg, Rienk H.; Salih, Abubakr A. M.; Brooks, Stephen J.; Whitehouse, Nicola J.; Karlatou-Charalampopoulou, Artemis; Wohlfarth, Barbara

    2015-11-01

    Sources and timing of freshwater forcing relative to hydroclimate shifts recorded in Greenland ice cores at the onset of Younger Dryas, ~12,800 years ago, remain speculative. Here we show that progressive Fennoscandian Ice Sheet (FIS) melting 13,100-12,880 years ago generates a hydroclimate dipole with drier-colder conditions in Northern Europe and wetter-warmer conditions in Greenland. FIS melting culminates 12,880 years ago synchronously with the start of Greenland Stadial 1 and a large-scale hydroclimate transition lasting ~180 years. Transient climate model simulations forced with FIS freshwater reproduce the initial hydroclimate dipole through sea-ice feedbacks in the Nordic Seas. The transition is attributed to the export of excess sea ice to the subpolar North Atlantic and a subsequent southward shift of the westerly winds. We suggest that North Atlantic hydroclimate sensitivity to FIS freshwater can explain the pace and sign of shifts recorded in Greenland at the climate transition into the Younger Dryas.

  15. Fennoscandian freshwater control on Greenland hydroclimate shifts at the onset of the Younger Dryas

    PubMed Central

    Muschitiello, Francesco; Pausata, Francesco S. R.; Watson, Jenny E.; Smittenberg, Rienk H.; Salih, Abubakr A. M.; Brooks, Stephen J.; Whitehouse, Nicola J.; Karlatou-Charalampopoulou, Artemis; Wohlfarth, Barbara

    2015-01-01

    Sources and timing of freshwater forcing relative to hydroclimate shifts recorded in Greenland ice cores at the onset of Younger Dryas, ∼12,800 years ago, remain speculative. Here we show that progressive Fennoscandian Ice Sheet (FIS) melting 13,100–12,880 years ago generates a hydroclimate dipole with drier–colder conditions in Northern Europe and wetter–warmer conditions in Greenland. FIS melting culminates 12,880 years ago synchronously with the start of Greenland Stadial 1 and a large-scale hydroclimate transition lasting ∼180 years. Transient climate model simulations forced with FIS freshwater reproduce the initial hydroclimate dipole through sea-ice feedbacks in the Nordic Seas. The transition is attributed to the export of excess sea ice to the subpolar North Atlantic and a subsequent southward shift of the westerly winds. We suggest that North Atlantic hydroclimate sensitivity to FIS freshwater can explain the pace and sign of shifts recorded in Greenland at the climate transition into the Younger Dryas. PMID:26573386

  16. Fennoscandian freshwater control on Greenland hydroclimate shifts at the onset of the Younger Dryas.

    PubMed

    Muschitiello, Francesco; Pausata, Francesco S R; Watson, Jenny E; Smittenberg, Rienk H; Salih, Abubakr A M; Brooks, Stephen J; Whitehouse, Nicola J; Karlatou-Charalampopoulou, Artemis; Wohlfarth, Barbara

    2015-01-01

    Sources and timing of freshwater forcing relative to hydroclimate shifts recorded in Greenland ice cores at the onset of Younger Dryas, ∼12,800 years ago, remain speculative. Here we show that progressive Fennoscandian Ice Sheet (FIS) melting 13,100-12,880 years ago generates a hydroclimate dipole with drier-colder conditions in Northern Europe and wetter-warmer conditions in Greenland. FIS melting culminates 12,880 years ago synchronously with the start of Greenland Stadial 1 and a large-scale hydroclimate transition lasting ∼180 years. Transient climate model simulations forced with FIS freshwater reproduce the initial hydroclimate dipole through sea-ice feedbacks in the Nordic Seas. The transition is attributed to the export of excess sea ice to the subpolar North Atlantic and a subsequent southward shift of the westerly winds. We suggest that North Atlantic hydroclimate sensitivity to FIS freshwater can explain the pace and sign of shifts recorded in Greenland at the climate transition into the Younger Dryas. PMID:26573386

  17. 75 FR 13497 - Freshwater Crawfish Tail Meat from the People's Republic of China: Rescission of Antidumping Duty...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-22

    ... to China Kingdom (Beijing) Import & Export Co., Ltd., Shanghai Ocean Flavor International Trading Co...'s Republic of China, 62 FR 48218 (September 15, 1997). On September 1, 2009, we published in the... Investigation; Opportunity to Request Administrative Review, 74 FR 45179 (September 1, 2009). On September...

  18. Convective Available Potential Energy of World Ocean

    NASA Astrophysics Data System (ADS)

    Su, Z.; Ingersoll, A. P.; Thompson, A. F.

    2012-12-01

    Here, for the first time, we propose the concept of Ocean Convective Available Potential Energy (OCAPE), which is the maximum kinetic energy (KE) per unit seawater mass achievable by ocean convection. OCAPE occurs through a different mechanism from atmospheric CAPE, and involves the interplay of temperature and salinity on the equation of state of seawater. The thermobaric effect, which arises because the thermal coefficient of expansion increases with depth, is an important ingredient of OCAPE. We develop an accurate algorithm to calculate the OCAPE for a given temperature and salinity profile. We then validate our calculation of OCAPE by comparing it with the conversion of OCAPE to KE in a 2-D numerical model. We propose that OCAPE is an important energy source of ocean deep convection and contributes to deep water formation. OCAPE, like Atmospheric CAPE, can help predict deep convection and may also provide a useful constraint for modelling deep convection in ocean GCMs. We plot the global distribution of OCAPE using data from the World Ocean Atlas 2009 (WOA09) and see many important features. These include large values of OCAPE in the Labrador, Greenland, Weddell and Mediterranean Seas, which are consistent with our present observations and understanding, but also identify some new features like the OCAPE pattern in the Antarctic Circumpolar Current (ACC). We propose that the diagnosis of OCAPE can improve our understanding of global patterns of ocean convection and deep water formation as well as ocean stratification, the meridional overturning circulation and mixed layer processes. The background of this work is briefly introduced as below. Open-ocean deep convection can significantly modify water properties both at the ocean surface and throughout the water column (Gordon 1982). Open-ocean convection is also an important mechanism for Ocean Deep Water formation and the transport of heat, freshwater and nutrient (Marshall and Schott 1999). Open-ocean convection may arise through strong surface buoyancy fluxes (Schott et al. 1996), or by thermobaric instability (Akitomo 1999a, b). Ingersoll (2005) demonstrated that thermobaric-induced deep convection is due to the abrupt release of ocean potential energy into kinetic energy. In atmospheric dynamics, Convective Available Potential Energy (CAPE) has long been an important thermodynamic variable (Arakawa and Schubert 1974) that has been used to forecast moist convection (Doswell and Rasmussen 1994) and to test the performance of GCMs (Ye et al. 1998). However, the development of a similar diagnostic in the ocean has received little attention.; World Ocean Convective Available Potential Energy distribution in North-Hemisphere Autumn (J/kg)

  19. Arctic Fresh Water Export and its Impact on Climate in the 20th and 21st Century

    NASA Astrophysics Data System (ADS)

    Koenigk, T.; Mikolajewicz, U.; Haak, H.; Jungclaus, J.

    2005-12-01

    Coupled IPCC experiments with the Max-Planck-Institute climate model ECHAM5/MPI-OM are used to analyse the changes in the fresh water export out of the Arctic. Furthermore, the impacts of these changes on climate are investigated. In the 20th century, 57 % of the simulated Arctic fresh water export (reference salinity is 34.8) into the North Atlantic Ocean takes place through Fram Strait, 32 % through the Canadian Archipelago and 11 % over the Barents Shelf. The variability is mainly governed by the ice export through Fram Strait and is highly affected by the atmospheric circulation. Large ice exports provoke a dramatic reduction in Labrador Sea surface salinity in the following years. Oceanic convection is decreased and ice cover is increased. As a consequence, the heat flux from ocean to atmosphere is below normal, which leads to significant negative temperature anomalies in the Labrador Sea. In the 21st century, our model results show a reduction of sea ice volume and an increase of precipitation and Arctic rivers runoff. Most of this additional fresh water is stored in the Arctic Ocean. The total Arctic fresh water export is only slightly changing until year 2100. However, a redistribution of the export occurs: The solid part becomes much smaller with time and plays no significant role anymore at the end of the 21st century. At the same time the fluid part increases. The export through the Canadian Archipelago rises by 0.025 Sverdrup, while the export over the Barents Shelf is reduced by 0.02 Sverdrup. The amount of fresh water exported through Fram Strait stays constant but the interannual variability is decreased by 25 %. The impact of the export through Fram Strait on Labrador Sea climate is thus strongly reduced. In contrast, the export through the Canadian Archipelago gains importance. The convection is reduced by about 40 % in the Greenland Sea and 60 % in the Labrador Sea. The reduction in the Labrador Sea can be explained by increased fresh water export through the Canadian Archipelago. In the Greenland Sea higher air and sea temperatures are the main reason for the decrease. In both regions the difference of precipitation and evaporation becomes larger and contributes to the decrease in convection. The meridional overturning circulation (MOC) at 30 degrees N declines from about 22 Sverdrup in the 20th century to 16 Sverdrup at the end of the 21st century. The reduction in the MOC leads to a much weaker warming in the northern North Atlantic in comparison to the surrounding areas.

  20. Position of the freshwater-saltwater interface in a coastal confined aquifer

    NASA Astrophysics Data System (ADS)

    Evans, T. B.; White, S. M.; Wilson, A. M.

    2014-12-01

    Delineating the position of the freshwater-saltwater interface is necessary for understanding submarine groundwater discharge and for assessing risks associated with saltwater intrusion, but most studies of the freshwater-saltwater interface focus on shallow surficial aquifers. Groundwater dynamics in coastal aquifers at depths greater than 5 m below land surface have rarely been assessed. The freshwater-saltwater interface in deeper confined aquifers is frequently positioned offshore, where it is difficult to locate or study. Our investigation was located at North Inlet, a wide, intertidal wetland southeast of Georgetown, SC. This site was ideal for studying the freshwater-saltwater interface at the embayment scale because the first major confined aquifer under the wetlands was accessible. Using electrical resistivity tomography, we were able to image the upper 20 to 30 m of sediment, including the first major confined aquifer. At North Inlet a 75 km2 island is bounded by extensive marsh and relict and modern barrier islands extending ~10 km seaward to the Atlantic Ocean. Surface and groundwater salinity throughout the marsh is 35 ppt. In order to get maximum depth penetration, surveys were conducted along dry land on the island and marsh surface with 10 m electrode spacing. Measured apparent resistivity varied in all surveys. A 20 Ohm-m resistivity layer at 25 m depth suggests that freshwater extends 335 m from the mainland. The presence of this freshwater indicates regional groundwater flow under the marsh or high rates of infiltration during precipitation events. Groundwater was saline to brackish (~10 Ohm-m) 1 km further out into the marsh at the next relict beach ridge at depths of 20 to 30 m. These results indicate that embayment scale groundwater flow plays an important role in providing low salinity pore-water to the marsh from beneath. The presence of fresh/brackish groundwater hundreds of meters from the mainland suggests that coastal confined aquifers transport freshwater significant distances. Freshwater could exist in analogous confined aquifers at shallow depths under the seafloor in other coastal systems.

  1. Glacial/interglacial changes in export production in a series of sediment cores spanning the Indian sector Antarctic Polar Front

    NASA Astrophysics Data System (ADS)

    Jaccard, S.; Thle, L.; Martinez-Garcia, A.; Studer, A.; Michel, E.; Mazaud, A.

    2014-12-01

    Export of organic carbon from surface waters of the Antarctic Zone of the Southern Ocean decreased during the last ice age, coinciding with declining atmospheric carbon dioxide (CO2) concentrations, signaling reduced exchange of CO2 between the ocean interior and the atmosphere. In contrast, in the Subantarctic Zone, export production increased into ice ages coinciding with rising dust fluxes, thus suggesting iron fertilization of Subantarctic phytoplankton. Recently developed XRF core-scanning methods permit paleoceanographic reconstructions on time-scales similar to ice core temperature and atmospheric carbon dioxide measurements. We have investigated the sedimentary distribution of various proxies allowing reconstructing export production in a series of sedimentary archives retrieved from the Indian Sector of the Southern Ocean spanning the Antarctic Polar Front in the vicinity of Kerguelen Island (Marion Dufresne Expeditions IndienSud-1 & 2). These high-resolution measurements are complemented with reconstruction of 230Th-normalized biogenic particle flux to the seafloor covering the last glacial termination.This contribution will explore the effects of Fe-fertilization on export production in an area remote from major dust sources. Furthermore, quantitative vertical flux determinations will allow comparing carbon export efficiency in the Indian Ocean with previously published records from the South Atlantic.

  2. 7 CFR 922.15 - Export.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... ORDERS; FRUITS, VEGETABLES, NUTS), DEPARTMENT OF AGRICULTURE APRICOTS GROWN IN DESIGNATED COUNTIES IN WASHINGTON Order Regulating Handling Definitions § 922.15 Export. Export means to ship apricots beyond...

  3. 7 CFR 922.15 - Export.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... ORDERS; FRUITS, VEGETABLES, NUTS), DEPARTMENT OF AGRICULTURE APRICOTS GROWN IN DESIGNATED COUNTIES IN WASHINGTON Order Regulating Handling Definitions § 922.15 Export. Export means to ship apricots beyond...

  4. 7 CFR 922.15 - Export.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE APRICOTS GROWN IN DESIGNATED COUNTIES IN WASHINGTON Order Regulating Handling Definitions § 922.15 Export. Export means to ship apricots beyond...

  5. 7 CFR 922.15 - Export.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE APRICOTS GROWN IN DESIGNATED COUNTIES IN WASHINGTON Order Regulating Handling Definitions § 922.15 Export. Export means to ship apricots beyond...

  6. 7 CFR 922.15 - Export.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE APRICOTS GROWN IN DESIGNATED COUNTIES IN WASHINGTON Order Regulating Handling Definitions § 922.15 Export. Export means to ship apricots beyond...

  7. 7 CFR 966.18 - Export.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE TOMATOES GROWN IN FLORIDA Order Regulating Handling Definitions § 966.18 Export. Export means shipment of tomatoes beyond the boundaries of the...

  8. 7 CFR 966.18 - Export.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... Orders; Fruits, Vegetables, Nuts), DEPARTMENT OF AGRICULTURE TOMATOES GROWN IN FLORIDA Order Regulating Handling Definitions § 966.18 Export. Export means shipment of tomatoes beyond the boundaries of the...

  9. 7 CFR 966.18 - Export.

    Co